A paper-based packaging material structure and packaging bag

Abstract

This utility model discloses a paper-based packaging material structure and packaging bag. The paper-based packaging material structure includes: a paper substrate layer, one surface of which has pores; an aqueous coating layer, which is disposed on one surface of the paper substrate layer and forms a continuous fixed film layer, the surface of the continuous fixed film layer away from the paper substrate layer being a smooth surface; and a printing layer, which is disposed on the smooth surface of the aqueous coating layer; wherein the gloss of the smooth surface measured at a preset angle is greater than 60 GU. By forming a high-gloss, smooth aqueous coating layer on a porous paper substrate as a printing substrate, this utility model solves the quality defects of traditional paper-based materials caused by surface roughness and uneven ink absorption, such as "missing dots" and "blurred printing," improving the clarity and gloss of printed materials and giving the packaging excellent printing quality.

Description

Technical Field

[0001] This utility model relates to the field of packaging materials technology, and in particular to a paper-based packaging material structure and packaging bag. Background Technology

[0002] In the current packaging industry, due to environmental protection and sustainable development requirements, paper-based materials (such as white cardboard and kraft paper) are gradually becoming an important alternative to traditional plastic films. However, the inherent characteristics of paper-based materials pose challenges to their application in high-end packaging. Specifically, the surface of paper-based materials is usually relatively rough and the fibers are loose, which leads to uneven absorption of printing inks and makes it difficult to form a smooth and continuous ink film. Therefore, during high-speed printing, printing defects such as "missing dots" (white spots) and "blurred edges" are prone to occur, seriously affecting the clarity of printed materials and the yield rate.

[0003] To address these issues, several improvement solutions exist. For example, pre-coating the paper base with a primer can improve surface wettability and ink adhesion to some extent, but its effect on gloss improvement is limited. Applying varnish after printing, while enhancing gloss, adds an extra step, complicates the process, and is prone to poor adhesion, powdering, and other quality problems, resulting in low overall efficiency. Alternatively, using PE / PP lamination or aluminized film can improve the material's smoothness and barrier properties, but it doesn't improve the printability of the paper base itself. More importantly, this composite structure introduces layers of plastic or metal that are difficult to recycle and degrade, increasing production costs and processing complexity.

[0004] Therefore, there is an urgent need in this field to provide a new paper-based packaging material structure that can improve the smoothness and gloss of paper to achieve high-quality printing, while maintaining the environmentally friendly properties of the material, and at the same time, the process is simple, thereby overcoming the above-mentioned defects. Utility Model Content

[0005] The main purpose of this utility model is to provide a paper-based packaging material structure and packaging bag to solve the above-mentioned technical problems.

[0006] The objective of this utility model can be achieved by adopting the following technical solution:

[0007] A paper-based packaging material structure includes: a paper substrate layer, one surface of which has pores; an aqueous coating layer disposed on one surface of the paper substrate layer to form a continuous fixed film layer, wherein the surface of the continuous fixed film layer away from the paper substrate layer is a smooth surface; and a printing layer disposed on the smooth surface of the aqueous coating layer; wherein the gloss of the smooth surface measured at a preset angle is greater than 60 GU.

[0008] The paper substrate layer, the water-based coating, and the printing layer are arranged sequentially from the inside out.

[0009] It also includes a heat-resistant varnish protective layer, which is disposed on the outer surface of the printed layer.

[0010] The thickness of the heat-resistant varnish protective layer is 1 to 5 micrometers.

[0011] It also includes a functional layer disposed on the inner surface of the paper substrate layer.

[0012] The functional layer is a heat-sealing layer, a barrier layer, or an aluminum-plated layer.

[0013] The paper substrate layer is made of white cardboard, kraft paper, coated paper, or offset paper.

[0014] The thickness of the aqueous coating is 2 to 15 micrometers.

[0015] The thickness of the aqueous coating is 10 to 15 micrometers.

[0016] A packaging bag includes a bag body, which, from the outside to the inside, comprises: a heat-resistant varnish protective layer, a printing layer, a water-based coating, a paper substrate layer, and a heat-sealing layer.

[0017] The outer surface of the paper substrate layer has pores, and the water-based coating forms a continuous fixed film layer on the outer surface of the paper substrate layer. The outer surface of the continuous fixed film layer is a smooth surface, and the printing layer is disposed on the smooth surface.

[0018] The beneficial technical effects of this utility model are as follows:

[0019] By forming a high-gloss, smooth, water-based coating on a porous paper substrate as a printing base, this invention solves the quality defects of traditional paper-based materials, such as "missing dots" and "blurred printing," caused by surface roughness and uneven ink absorption. This improves the clarity and gloss of printed materials, resulting in superior printing quality for packaging. Compared to existing technologies, this invention integrates surface smoothing and high-gloss functions, replacing complex processes such as traditional lamination or post-printing varnishing, effectively simplifying the production process and reducing manufacturing costs. Simultaneously, the use of a water-based coating maintains the material's environmentally friendly and recyclable characteristics, meeting the requirements of sustainable development in the packaging industry. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic cross-sectional view of the paper-based packaging material structure provided in an embodiment of the present utility model;

[0022] Figure 2 This is a front view schematic diagram of the packaging bag provided in an embodiment of the present utility model;

[0023] Figure 3 This is a schematic cross-sectional view of the bag body in the packaging bag provided in an embodiment of the present utility model.

[0024] Explanation of reference numerals in the attached figures:

[0025] In the diagram: 10-paper substrate layer, 20-water-based coating, 30-printing layer, 40-heat-resistant varnish protective layer, 50-functional layer, 51-heat-sealing layer, 101-bag body. Detailed Implementation

[0026] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present utility model.

[0027] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0028] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0029] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0030] like Figure 1 As shown, this utility model embodiment provides a paper-based packaging material structure. This structure aims to solve the problems of rough surface and poor printability of existing paper-based materials by introducing a water-based coating 20 to improve the printability of the packaging material. The structure includes: a paper substrate layer 10, one surface of which has pores; a water-based coating 20, which is disposed on one surface of the paper substrate layer 10 and forms a continuous fixed film layer, the surface of which is smooth away from the paper substrate layer 10; and a printing layer 30, which is disposed on the smooth surface of the water-based coating 20; wherein the gloss of the smooth surface measured at a preset angle is greater than 60 GU.

[0031] In this embodiment, the paper-based packaging material structure includes a paper substrate layer 10, a water-based coating 20, and a printing layer 30.

[0032] Specifically, the paper substrate layer 10 is the foundation of the entire packaging material structure, playing a major mechanical support role. In this embodiment, the paper substrate layer 10 is made of paper commonly used in the packaging industry. Because it is made of interwoven plant fibers, one of its surfaces naturally has microscopic pores and roughness. This makes it difficult for ink to form a continuous and smooth ink film when printing directly on it, easily resulting in printing defects such as "missing dots" and "blurred appearance," and also resulting in low surface gloss.

[0033] To address the aforementioned issues, this embodiment provides an aqueous coating 20 on a porous surface of the paper substrate layer 10. This aqueous coating 20 is uniformly applied to the surface of the paper substrate layer 10 using a coating process (e.g., by a doctor blade, anilox roller, or grooved roller). After drying and curing, the aqueous coating 20 forms a continuous, fixed film on the surface of the paper substrate layer 10. This film effectively fills and seals the pores on the surface of the paper substrate layer 10 and levels rough surfaces, thereby forming a smooth surface away from the paper substrate layer 10. This smooth surface provides a dense, uniform, and high-quality printing substrate for subsequent printing processes.

[0034] Crucially, the water-based coating 20 in this embodiment is a high-gloss water-based coating 20, which, after curing, forms a smooth surface with high gloss. When measured using a gloss meter at a preset angle (e.g., 60 degrees), the gloss of this smooth surface is greater than 60 GU. In a specific application, a gloss of 67.5 GU can be used, representing an improvement of over 160% compared to the gloss of the untreated paper substrate layer 10 surface (approximately 25.84 GU), thus visually presenting a mirror-like effect.

[0035] Finally, the printing layer 30 is disposed on the smooth surface of the water-based coating 20. Due to the excellent flatness and high gloss of this smooth surface, the ink can be well wetted and spread, forming a printed pattern with clear edges and rich colors. This not only effectively avoids the defects commonly found when printing directly on traditional paper substrates, but also greatly improves the clarity of the printed matter, meeting the high-quality requirements of high-speed printing.

[0036] In summary, this embodiment successfully constructs a high-gloss, high-printing-quality paper-based packaging material structure by applying a water-based coating 20 that forms a high-gloss, smooth surface to the surface of a porous paper substrate layer 10, and then printing on this smooth surface. This effectively solves the shortcomings of the prior art and provides an environmentally friendly solution for the packaging market.

[0037] In this embodiment, the basis weight of the paper substrate layer 10 can be 40 g / m². 2 Up to 150g / m 2 To provide suitable mechanical support performance.

[0038] In this embodiment, the water-based coating 20 can use water-based acrylic emulsion or water-based polyurethane emulsion as the main film-forming system, and can be supplemented with high refractive index gloss additives, film-forming aids, leveling agents, and environmentally friendly crosslinking agents to ensure that the coating can form a film layer with excellent optical and physical properties after drying. This water-based coating 20 is a pure water-based system, contains no organic solvents, and is environmentally friendly and biodegradable. The water-based coating 20 can be applied to one side on a coating machine using a doctor blade, an anilox roller, or a grooved roller, offering strong process adaptability.

[0039] In addition to providing a smooth, high-gloss surface, the water-based coating 20, after partially penetrating into the fiber gaps on the surface of the paper substrate layer 10 during application and curing, effectively improves the stiffness, folding endurance, and tear resistance of the paper substrate layer 10. This enhances the adaptability and reliability of the paper substrate layer 10 during subsequent folding, creasing, heat sealing, and transportation, making the packaging less prone to damage during forming and use.

[0040] In this embodiment, the smooth surface is particularly suitable for high-speed printing processes such as water-based gravure and flexographic printing, enabling good ink wetting and adhesion, and effectively improving the uniformity and edge sharpness of the ink film. The printing layer 30 can be directly applied to this smooth surface without additional primer treatment, thereby simplifying the production process and reducing production costs. The gloss of this smooth surface is measured using conventional methods in the art, and will not be described in detail here.

[0041] In one embodiment, the paper substrate layer 10, the water-based coating 20, and the printing layer 30 are arranged sequentially from the inside to the outside.

[0042] In this embodiment, the paper substrate layer 10, the water-based coating 20, and the printing layer 30 are stacked sequentially in a specific order. Specifically, from the inside out, they are: paper substrate layer 10, water-based coating 20, and printing layer 30.

[0043] This hierarchical distribution clearly defines the functional positioning of each layer. The paper substrate layer 10, as the innermost base, provides support for the entire structure. The water-based coating 20, as the intermediate layer, directly covers the outer surface of the paper substrate layer 10, playing a crucial role in connecting the upper and lower layers. It fills the pores of the paper substrate internally and forms a smooth surface externally, providing an excellent substrate for printing the printing layer 30. The printing layer 30, as the outermost graphic display layer, is placed on the smooth surface of the water-based coating 20, and its printed content directly faces the consumer. This hierarchical structure from the inside out is clear and reasonable. In practical applications, "inner" refers to the side facing the packaging contents, while "outer" refers to the side facing the external environment.

[0044] In one embodiment, a heat-resistant varnish protective layer 40 is also included, which is disposed on the outer surface of the printed layer 30.

[0045] In this embodiment, in addition to the paper substrate layer 10, water-based coating 20, and printing layer 30 arranged sequentially from the inside out, a transparent heat-resistant varnish protective layer 40 is also included. This heat-resistant varnish protective layer 40 is disposed on the outer surface of the printing layer 30, thus becoming the outermost layer of the entire paper-based packaging material structure.

[0046] The main function of the heat-resistant varnish protective layer 40 is to protect the underlying printed layer 30 from external environmental factors (such as ultraviolet rays, oxygen, moisture, grease, etc.) and from damage caused by friction and scratching during subsequent processing, transportation, and use. By setting this heat-resistant varnish protective layer 40, problems such as fading, blurring, ink smudging, or damage to the printed pattern can be effectively prevented, improving the scratch resistance, weather resistance, and temperature resistance of the printed pattern, thereby extending the appearance retention time of the packaged product and improving the product's shelf life and end-use durability.

[0047] In one specific implementation, a varnish or clear coat with acrylic or polyurethane materials as the main film-forming system can be formed by coating or spraying.

[0048] In one embodiment, the thickness of the heat-resistant varnish protective layer 40 is 1 to 5 micrometers.

[0049] In this embodiment, the limitation on the thickness of the heat-resistant varnish protective layer 40 is based on a comprehensive consideration of function, cost, and processing technology. If the thickness of the heat-resistant varnish protective layer 40 is less than 1 micrometer, a complete and dense protective film cannot be formed, and its protective effect on the printed layer 30 will be greatly reduced, making it difficult to effectively resist external physical scratches and chemical corrosion. If the thickness of the heat-resistant varnish protective layer 40 is greater than 5 micrometers, although the protective performance is stronger, it will unnecessarily increase the material cost and the overall thickness and weight of the entire packaging material.

[0050] Therefore, the thickness of the heat-resistant varnish protective layer 40 is set between 1 and 5 micrometers. This thickness range ensures that the heat-resistant varnish protective layer 40 provides sufficient and durable protection for the printed pattern underneath, while avoiding the negative impacts on cost and process caused by excessive thickness, thus achieving the best combination of protective performance and economic benefits.

[0051] In this embodiment, the heat resistance of the heat-resistant varnish protective layer 40 is primarily designed to accommodate the heat-sealing process of the packaging bag on an automated packaging line. During typical heat-sealing operations, the material near the sealing area may be briefly exposed to temperatures exceeding 150°C. The heat-resistant varnish protective layer in this embodiment ensures that the printed appearance of the non-sealed area remains unaffected under such process conditions.

[0052] In one embodiment, a functional layer 50 is further included, which is disposed on the inner surface of the paper substrate layer 10.

[0053] In this embodiment, in addition to the structure comprising a heat-resistant varnish protective layer 40, a printing layer 30, a water-based coating 20, and a paper substrate layer 10, a functional layer 50 is further included. This functional layer 50 is disposed on the inner surface of the paper substrate layer 10. Here, "inner surface" refers to the side of the paper substrate layer 10 facing the packaging contents, i.e., the surface opposite to the side coated with the water-based coating 20.

[0054] By adding this functional layer 50 to the inner surface of the paper substrate layer 10, specific properties, such as heat-sealing and barrier properties, can be introduced into the entire packaging material structure, which are not present in the paper substrate layer 10 alone. The introduction of this functional layer 50 enables the paper-based packaging material structure of this embodiment to not only have excellent printing effects but also possess the functionality required for practical packaging applications. Therefore, it is suitable for packaging fields requiring sealing or specific protection of contents, such as the manufacture of food packaging bags and sealed packaging boxes.

[0055] In one embodiment, the functional layer 50 is a heat-sealing layer 51, a barrier layer, or an aluminum-plated layer.

[0056] In this embodiment, the functional layer 50 disposed on the inner surface of the paper substrate layer 10 can be selected from at least one of the following, depending on the specific requirements of the final product: heat-sealing layer 51, barrier layer or aluminum plating layer.

[0057] In one specific embodiment, the functional layer 50 is a heat-sealable layer 51, which enables the packaging material to be sealed by heat and pressure, and is key to the production of flexible packaging such as resealable bags and stand-up pouches. For example, the heat-sealable layer 51 can be a water-based acrylic layer, or other heat-sealable polymer layers (such as ethylene-acrylic acid copolymer (EAA) layers or polyhydroxyalkanoate (PHA) layers), which provide excellent adhesion and heat-sealing strength. In one specific embodiment, the thickness of the heat-sealable layer 51 can be 2 to 5 micrometers (dry basis weight of 3 to 10 g / m³). 2 ).

[0058] In another specific embodiment, the functional layer 50 is a barrier layer, whose main function is to prevent the penetration of substances such as oxygen, water vapor, oil, or odors, so as to protect the product (especially food) inside the packaging from spoilage and extend its shelf life.

[0059] In another specific embodiment, the functional layer 50 is an aluminum-plated layer, that is, an extremely thin layer of metallic aluminum is laminated onto the inner surface of the paper substrate layer 10. This aluminum-plated layer not only provides excellent barrier properties against light, oxygen, and moisture, but also imparts a metallic luster to the inside of the packaging, enhancing the product's perceived quality.

[0060] By selecting or combining the different types of functional layers 50 described above, the paper-based packaging material of this embodiment can flexibly meet diverse and high-performance packaging requirements.

[0061] In one embodiment, the paper substrate layer 10 is white cardboard, kraft paper, coated paper, or offset paper.

[0062] In this embodiment, these paper types all possess good mechanical properties and suitability as substrates. White cardboard has high stiffness and a smooth surface, making it suitable for high-end packaging; kraft paper has high strength and tear resistance, often used for packaging requiring high load-bearing capacity; coated paper has a smooth and white surface, providing a good printing base, and after applying the water-based coating 20, it achieves an even better mirror effect; offset paper has low elasticity and uniform ink absorption, also commonly used for packaging and printing. Selecting these specific types of paper as the substrate layer ensures that the packaging material has reliable physical support strength and basic printing performance, laying a solid foundation for the subsequent application of the water-based coating 20 and the final high-quality printing effect. In practical implementation, white kraft paper or coated paper with moderate stiffness can be selected as the paper substrate layer 10.

[0063] In one embodiment, the thickness of the aqueous coating 20 is 2 to 15 micrometers.

[0064] In this embodiment, the thickness of the continuous fixed film layer formed by the water-based coating 20 after drying and curing is controlled within the range of 2 to 15 micrometers (μm).

[0065] If the coating thickness is less than 2 micrometers, the coating may not be sufficient to completely fill the pores on the paper surface and form a sufficiently smooth, continuous film, resulting in limited improvement in gloss and little effect on printability. Conversely, if the coating thickness exceeds 15 micrometers, although the smoothness is higher, it increases material costs and the drying load in production, reducing production efficiency.

[0066] Therefore, controlling the thickness of the water-based coating 20 to 2 to 15 micrometers is a balance achieved between ensuring high gloss and smoothness, improving printability, controlling production costs, and ensuring processing adaptability.

[0067] In one embodiment, the thickness of the aqueous coating 20 is 10 to 15 micrometers.

[0068] In this embodiment, when the thickness of the water-based coating 20 reaches 10 micrometers or more, its leveling and filling effects are more sufficient, ensuring that the micropores on the surface of the paper substrate layer 10 are completely covered, thereby forming an extremely smooth and dense printing substrate. At the same time, controlling the upper limit of the thickness to 15 micrometers can effectively avoid problems such as prolonged drying time, increased energy consumption, and unnecessary increase in material costs caused by excessive coating thickness.

[0069] like Figure 2 and Figure 3 As shown, corresponding to the above-mentioned paper-based packaging material structure, this utility model embodiment also provides a packaging bag, which is composed of a bag body 101. The bag body 101 includes, from the outside to the inside, a heat-resistant varnish protective layer 40, a printing layer 30, a water-based coating 20, a paper substrate layer 10, and a heat-sealing layer 51. The outer surface of the paper substrate layer 10 has pores, and the water-based coating 20 forms a continuous fixed film layer on the outer surface of the paper substrate layer 10. The outer surface of the continuous fixed film layer is a smooth surface, and the printing layer 30 is disposed on the smooth surface.

[0070] In one embodiment, the bag body 101 is made of a paper-based packaging material structure through a bag-making process (e.g., winding, center sealing, and end sealing). The layered structure of the bag body 101, from the outside to the inside (i.e., from the side in contact with the external environment to the side in contact with the contents of the packaging), includes, in sequence: a heat-resistant varnish protective layer 40, a printing layer 30, a water-based coating 20, a paper substrate layer 10, and a heat-sealing layer 51.

[0071] The specific structure and function of each layer are as follows:

[0072] Heat-resistant varnish protective layer 40: As the outermost layer of the packaging bag, it is directly exposed to the external environment. It is a transparent protective coating whose main function is to protect the printed pattern underneath from friction and scratches during transportation and shelf display, while resisting the effects of moisture and ultraviolet rays to prevent the pattern from fading.

[0073] Printed layer 30: Located below the heat-resistant varnish protective layer 40, it carries the product's brand logo, patterns, and explanatory text, among other visual information.

[0074] Water-based coating 20: Located between the printing layer 30 and the paper substrate layer 10. It is applied directly to the outer surface of the paper substrate layer 10 and, after drying and curing, forms a continuous, fixed film layer. The function of this film layer is to fill and seal the pores of the paper substrate layer 10, forming an extremely smooth outer surface (i.e., a smooth surface), providing an ideal substrate for the printing layer 30 above, thereby achieving a high-definition, high-gloss printing effect.

[0075] Paper substrate layer 10: As the structural support skeleton of the entire packaging bag, it provides the necessary stiffness and mechanical strength, so that the packaging bag has a good shape and load-bearing capacity after it is formed.

[0076] Heat-sealing layer 51: As the innermost layer of the packaging bag, it comes into direct contact with the contents. This layer enables the packaging material to be sealed by heating and pressurizing, and is a key functional layer for sealing the center seam and both ends of the bag body 101 to form a complete sealed container.

[0077] In summary, the packaging bag of this embodiment organically integrates a structure with a smooth surface (water-based coating + paper substrate layer) with an outer heat-resistant varnish protective layer 40, a printing layer 30, and an inner heat-sealing layer 51 to obtain an environmentally friendly packaging product with a complete structure and full functionality.

[0078] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this utility model, and these modifications or substitutions should all be covered within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the scope of the claims.

Claims

1. A paper-based packaging material structure, characterized in that, include: A paper substrate layer, one surface of which has pores; A water-based coating is applied to one surface of the paper substrate layer to form a continuous fixed film layer, wherein the surface of the continuous fixed film layer away from the paper substrate layer is a smooth surface. A printed layer is disposed on the smooth surface of the water-based coating; The gloss level of the smooth surface measured at a preset angle is greater than 60 GU.

2. The paper-based packaging material structure according to claim 1, characterized in that, The paper substrate layer, the water-based coating, and the printing layer are arranged sequentially from the inside out.

3. The paper-based packaging material structure according to claim 2, characterized in that, It also includes a heat-resistant varnish protective layer, which is disposed on the outer surface of the printed layer.

4. The paper-based packaging material structure according to claim 3, characterized in that, The thickness of the heat-resistant varnish protective layer is 1 to 5 micrometers.

5. The paper-based packaging material structure according to claim 3, characterized in that, It also includes a functional layer disposed on the inner surface of the paper substrate layer.

6. The paper-based packaging material structure according to claim 5, characterized in that, The functional layer is a heat-sealing layer, a barrier layer, or an aluminum-plated layer.

7. The paper-based packaging material structure according to claim 1, characterized in that, The paper substrate layer is made of white cardboard, kraft paper, coated paper, or offset paper.

8. The paper-based packaging material structure according to claim 1, characterized in that, The thickness of the aqueous coating is 2 to 15 micrometers.

9. The paper-based packaging material structure according to claim 1, characterized in that, The thickness of the aqueous coating is 10 to 15 micrometers.

10. A packaging bag, characterized in that, The bag includes a bag body, which, from the outside in, comprises: a heat-resistant varnish protective layer, a printing layer, a water-based coating, a paper substrate layer, and a heat-sealing layer. The outer surface of the paper substrate layer has pores, and the water-based coating forms a continuous fixed film layer on the outer surface of the paper substrate layer. The outer surface of the continuous fixed film layer is a smooth surface, and the printing layer is disposed on the smooth surface.

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