A coating composition, interface barrier coating and multilayer coated packaging paperboard

Abstract

The application belongs to the technical field of packaging materials, and relates to a coating composition, an interface isolation coating and a multi-layer coated packaging paperboard; the coating composition comprises water and a solid component, the solid component comprises polyvinyl alcohol, a non-ionic polyurethane dispersion and a sheet-shaped nano filler, the three components are precisely compounded, the coating formed after the coating composition is dried has excellent isolation performance, can effectively inhibit small molecule migration, and due to the fact that the coating does not contain common functional components such as a crosslinking agent, a hydrophobic agent and a fluorine-containing compound, the coating also has chemical inertness and suitable surface energy, when the coating is applied to the multi-layer coated packaging paperboard, does not react with upper and lower layer acid and alkali substances, a crosslinking agent and the like in any chemical reaction, and does not affect the original physical and chemical properties of the paperboard.

Description

Technical Field

[0001] This application belongs to the field of packaging materials technology, and relates to a coating composition, an interface isolation coating, and a multilayer coated packaging paperboard. Background Technology

[0002] In the manufacturing process of high-end printed and functional packaging paperboard, to meet the comprehensive needs of end products for waterproofing, oil resistance, antibacterial properties, and exquisite decorative effects, a single coating structure often cannot simultaneously address all performance indicators. Therefore, multi-layer coating processes have become the industry mainstream. A typical process flow includes: first, applying a primer coating to the paperboard substrate, then printing to form the graphic layer, and finally applying a topcoat to impart functions such as waterproofing, oil resistance, or tactile adjustment.

[0003] However, the aforementioned multilayer coating process faces severe interlayer compatibility issues in practical applications, mainly manifested in the following three aspects: First, interlayer penetration interference. Small molecules such as surfactants, unreacted monomers, or plasticizers remaining in the lower coating layer can migrate upwards to the upper layer during drying or storage, leading to pinholes, poor wetting, or functional failure in the upper coating layer. Second, interface reaction damage. Crosslinking agents, acid and alkali components in the upper coating layer may undergo unexpected chemical reactions with the lower layer, causing coating discoloration, decreased adhesion, or even damage to specific functions of the lower layer (such as fluorescent anti-counterfeiting properties). Third, deterioration of appearance quality. If the surface energy of the lower coating layer is too high or too low, it will directly affect the leveling of the upper coating layer, resulting in appearance defects such as orange peel, pinholes, and uneven gloss on the coating surface.

[0004] To address the aforementioned issues, existing technologies typically attempt to introduce a "retaining primer" or "barrier layer" between the layers. Examples include high-barrier polyvinyl alcohol (PVA) coatings or high-adhesion polyacrylate primers. However, these existing retaining materials inherently possess strong functional tendencies; for instance, PVA coatings exhibit extremely high polarity and hydrophilicity, while polyacrylate primers often provide high adhesion through strong anchoring groups. These inherent chemical properties make the retaining layer itself a new interfering variable, unable to maintain the original physicochemical state of the upper and lower layer interfaces. In other words, existing technologies lack a truly "inert" chemically sound, "neutral" interfacial retaining material that neither alters the surface energy of the cardboard and the upper and lower coatings, nor fails to provide a purely physical barrier function.

[0005] Therefore, developing a coating composition with excellent barrier properties, chemical inertness, and no disturbance to interlayer surface energy is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this application is to provide a coating composition, an interface isolation coating, and a multilayer coated packaging paperboard. The interface isolation coating formed by the coating composition has excellent barrier properties without containing common functional components such as crosslinking agents, hydrophobic agents, and fluorinated compounds. It also has the characteristics of chemical inertness and no interference with interlayer surface energy.

[0007] To achieve this objective, the present application adopts the following technical solution: In a first aspect, this application provides a coating composition comprising water and solid components, wherein the solid components, based on a total mass of 100%, comprise: Polyvinyl alcohol 30-50%; Nonionic polyurethane dispersion 20-40%; Nanofillers: 10-30%.

[0008] This application addresses the problems of interlayer penetration interference, interface reaction damage, and deterioration of appearance quality in existing multilayer coated paperboards by providing a coating composition with "functional neutrality" characteristics. It has chemical inertness and suitable surface energy, and achieves efficient isolation function through a purely physical mechanism without relying on chemical reactions or surface energy modification. Specifically, this application proposes for the first time the concept of "non-interference" pure interface isolation. Unlike existing coatings designed to impart specific functions such as waterproofing, oil resistance, or enhanced adhesion to cardboard, the coating composition provided in this application uses polyvinyl alcohol (PVA) and nonionic polyurethane dispersion (PUD) for precise compounding. The PVA acts as a physical isolation framework, forming a continuous, dense, and completely transparent film. The PUD precisely adjusts the final surface energy of the film to the neutral range (approximately 38-42). The coating (mN / m) ensures good wettability of both upper and lower coating liquids after formation. The addition of sheet-like nanofillers creates a "maze effect" in the film, effectively extending the migration path of small molecules and constructing a highly efficient dynamic physical barrier for small molecules. This barrier can inhibit over 90% of small molecule migration, exhibiting excellent barrier properties. Furthermore, since this application does not use any crosslinking agents, hydrophobic agents (such as waxes or silicone oils), fluorinated compounds, UV absorbers, antibacterial agents, or other additives with specific functions, it truly achieves chemical inertness. This ensures that the formed interfacial isolation coating does not react with the upper and lower coating materials, and it does not disturb the interlayer surface energy. Both upper and lower coating liquids can spread normally without causing pinholes, orange peel, or decreased adhesion. In other words, it does not change the inherent chemical properties of the cardboard and the upper and lower coatings, nor does it introduce new interfering variables, fundamentally solving the problem of the isolation layer itself becoming a process hazard.

[0009] In this application, the amount of polyvinyl alcohol used can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, or 50%, etc.

[0010] In this application, the amount of the nonionic polyurethane dispersion can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, or 40%, etc.

[0011] In this application, the amount of the sheet-like nanofiller can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, or 30%, etc.

[0012] In some specific embodiments, the solid content of the coating composition is 15-25%, such as 15%, 17%, 19%, 21%, 23%, or 25%.

[0013] In some specific embodiments, the degree of alcoholysis of the polyvinyl alcohol is 86-89%, such as 86%, 86.5%, 87%, 87.5%, 88%, 88.5%, or 89%.

[0014] In some specific embodiments, the sheet-like nanofiller includes sheet-like kaolin.

[0015] In some specific embodiments, the aspect ratio of the sheet-like nanofiller is ≥50, such as 50, 52, 54, 56, 58, 60, 65, 70, 75 or 80.

[0016] In this application, the aspect ratio of the sheet-like nanofiller is determined using scanning electron microscopy (SEM) image analysis. Specifically, an appropriate amount of sheet-like nanofiller is dispersed in anhydrous ethanol and ultrasonically dispersed until a uniform suspension is reached, with the mass percentage of sheet-like nanofiller in the suspension being 0.05%. A small amount of the suspension is dropped onto the SEM sample stage, dried at room temperature, and then sputter-coated with gold. According to GB / T 43196-2023, particle morphology images are obtained using scanning electron microscopy. At least 200 complete single-piece particles are randomly selected, and their diameter (d) and thickness (t) are measured respectively. The aspect ratio d / t of a single particle is calculated, and the arithmetic mean of all measured values ​​is taken as the aspect ratio of the batch of sheet-like nanofiller. In some specific embodiments, the D of the sheet-like nanofiller... 50 The sheet diameter is ≤0.5 μm, such as 0.5 μm, 0.45 μm, 0.4 μm, 0.35 μm, 0.3 μm, 0.25 μm, 0.2 μm or 0.15 μm, etc.

[0017] In some specific embodiments, the coating composition also includes a leveling agent.

[0018] In some specific embodiments, the total mass of the solid components is 100%, and the mass percentage of the leveling agent is 1-5%, such as 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0019] In some specific embodiments, the leveling agent includes acetylenic diol nonionic surfactants.

[0020] In this application, the leveling agent is used to provide good dynamic wetting ability and ensure that the coating is free of pinholes under high-speed coating. This application prefers acetylenic diol nonionic surfactants as leveling agents because they have nonionic properties and will not remain on the surface and affect interlayer adhesion.

[0021] Secondly, this application provides a method for preparing the coating composition as described in the first aspect, the method comprising: mixing solid components uniformly in water, filtering, and obtaining the coating composition.

[0022] In some specific embodiments, the preparation method of the coating composition includes the following steps: (1) Mix polyvinyl alcohol with water accounting for 25-40% of the total water mass to obtain a polyvinyl alcohol aqueous solution; (2) In a high-speed disperser, the sheet-like nanofiller is mixed with a polyvinyl alcohol aqueous solution accounting for 20-40% of the total mass of the polyvinyl alcohol aqueous solution obtained in step (1), and dispersed at a high speed of 2000-4000 rpm for 20-40 min to obtain a stable, non-agglomerated pre-dispersed slurry. (3) Under low-speed stirring at 400~600 rpm, the remaining polyvinyl alcohol solution obtained in step (1), nonionic polyurethane dispersion, leveling agent and residual water are slowly added to the pre-dispersed slurry obtained in step (2) in sequence, and stirring is continued until completely uniform. The mixture is then filtered through a 100~300 mesh screen to obtain the coating composition.

[0023] Thirdly, this application provides an interface isolation coating, which is formed by leveling and drying the coating composition as described in the first aspect.

[0024] In some specific embodiments, the average pore size of the interface isolation coating is ≤10 nm.

[0025] In this application, the pore size of the interface isolation coating can be obtained by gas adsorption method (BET / BJH), specifically by analyzing the amount of specific gas (such as nitrogen) adsorbed by the interface isolation coating to determine the specific surface area and pore size distribution.

[0026] Fourthly, this application provides an application of the interface isolation coating as described in the third aspect in multilayer coated packaging paperboard.

[0027] The interface isolation coating described in the third aspect of this application is applicable not only to the different functional layers (printing layer, waterproof layer, oil-proof layer, etc.) of multilayer coated packaging paperboard, but also to the paperboard and functional layers, serving as a pure interface isolation layer that does not interfere with the function and appearance of the upper and lower layers.

[0028] Fifthly, this application provides a multi-layer coated packaging paperboard, which includes a paperboard, an interface isolation coating as described in the third aspect, and an upper functional layer arranged sequentially.

[0029] In some specific embodiments, an underlying functional layer is also included between the cardboard and the interface isolation coating.

[0030] In this application, the upper functional layer and the lower functional layer are each independently an oil-based functional coating and / or a water-based functional coating, including but not limited to ink printing layers, waterproof layers, oil-proof layers, etc. After the interface isolation coating described in the third aspect dries, the surface area of ​​the film can be precisely controlled at 40±2 mN / m. This value is exactly between that of common ink printing layers (36~40 mN / m) and water-based functional coatings (40~44 mN / m), thereby achieving bidirectional compatibility.

[0031] In some specific embodiments, the areal density of the interface isolation coating is 1~3 g / m³. 2 For example, 1 g / m 2 1.2g / m 2 1.4 g / m 2 1.6 g / m 2 1.8 g / m 2 2 g / m 2 2.2 g / m 2 2.4 g / m 2 2.6 g / m 2 2.8 g / m 2 Or 3 g / m 2 The interface isolation coating is extremely thin, so it does not change the original stiffness and feel of the cardboard and has minimal impact on the physical properties of the cardboard.

[0032] Fifthly, this application provides a method for preparing a multilayer coated packaging paperboard as described in the fourth aspect, the method comprising: coating the paperboard surface with a coating composition as described in the fourth aspect, drying it, and then coating it with an upper functional layer material to obtain the multilayer coated packaging paperboard.

[0033] In some specific embodiments, the coating may be performed using a doctor blade, air knife, gravure, or flexographic coating machine.

[0034] In some specific embodiments, the drying temperature is 80~100℃, such as 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃ or 100℃.

[0035] Compared with the prior art, this application has the following advantages: (1) The coating composition provided in this application does not rely on chemical reactions or surface energy modification, but achieves the isolation function through a purely physical mechanism. It utilizes polyvinyl alcohol, nonionic polyurethane dispersion and sheet-like nanofiller to form a dense interfacial isolation coating with an average pore size ≤10 nm, thereby effectively preventing the migration of small molecules (surfactants, residual monomers) with a migration inhibition rate ≥90%. (2) The components contained in the coating composition provided in this application are all chemically inert or have been passivated by physical means, and common functional components such as crosslinking agents, hydrophobic agents, and fluorine-containing compounds are explicitly excluded, ensuring the "non-interference" characteristic. At the same time, the overall pH value of the system is neutral (6.5~7.5), so when applied in multi-layer coated packaging paperboard, it will not react with the acid and alkali substances, crosslinking agents, etc. of the upper and lower layers, and has chemical inertness. (3) The coating composition provided in this application is precisely compounded with polyvinyl alcohol and nonionic polyurethane dispersion. After drying, the surface energy of the film layer is precisely controlled at 40±2 mN / m. This value is exactly between common printing ink layers (36~40 mN / m) and water-based functional coatings (40~44 mN / m), thus achieving bidirectional compatibility. Detailed Implementation

[0036] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0037] The detailed information of some of the raw materials involved in the specific implementation method is shown below: (1) Polyvinyl alcohol PVA-1: Degree of alcoholysis is 88%, grade is PVA-1788; PVA-2: Degree of alcoholysis is 84%, grade is PVA-1784; PVA-3: Degree of alcoholysis is 90%, grade is PVA-1790.

[0038] (2) Nonionic polyurethane dispersion PUD: Purchased from Wanhua Chemical Group Co., Ltd., brand name Wannate® WPU-801.

[0039] (3) Sheet-shaped nanofillers Flake kaolin-1: Aspect ratio of 55, D 50 The sheet diameter is 0.3 μm; Flake kaolin-2: Aspect ratio of 40, D 50 The sheet diameter is 0.5 μm.

[0040] (4) Leveling agent Acetylene diol nonionic surfactant: purchased from Evonik, brand name Surfynol® 420.

[0041] Examples 1-6 and Comparative Examples 1-4 Examples 1-6 and Comparative Examples 1-4 each provide a coating composition, all of which contain water and solid components, with a solid content of 20%. The total mass of the solid components is 100%. The components included in the solid components are shown in Table 1. In Table 1, the amount of each component is expressed in "%". Table 1 The preparation methods of the coating compositions provided in Examples 1-6 and Comparative Examples 1-4 include the following steps: (1) Mix polyvinyl alcohol with water accounting for 33% of the total water mass to obtain a polyvinyl alcohol aqueous solution; (2) In a high-speed disperser, the sheet-like nanofiller is mixed with a polyvinyl alcohol aqueous solution accounting for 30% of the total mass of the polyvinyl alcohol aqueous solution obtained in step (1), and dispersed at a high speed of 3000 rpm for 30 min to obtain a stable, non-agglomerated pre-dispersed slurry. (3) Under low-speed stirring at 500 rpm, the remaining polyvinyl alcohol solution obtained in step (1), nonionic polyurethane dispersion, leveling agent and remaining water are slowly added to the pre-dispersed slurry obtained in step (2) in sequence, and stirring is continued until completely uniform. The mixture is then filtered through a 200-mesh filter to obtain the coating composition.

[0042] Performance testing: (1) Chemical inertness: The coating composition was diluted with deionized water to a solid content of 10%, and its pH value was measured using a pH meter.

[0043] (2) Isolation performance: First, multi-layer coated paperboard is prepared. The preparation method includes the following steps: ① Paperboard substrate preparation: Select a basis weight of 300 g / m 2 ① Use coated paperboard as the substrate, cut to A4 size, ensuring a smooth and contamination-free surface; ② Apply an interface isolation coating: Apply the coating composition to the surface of the paperboard substrate using a bar coater, controlling the wet film coating amount to achieve a dry coating amount of 2 g / m². 2, and hot-air dried at 90°C to obtain a paperboard coated with an interface isolation coating; ③ Coating the upper functional layer: on the surface of the dried interface isolation coating, an upper functional layer material (such as a water-based waterproof coating) is coated with a wire bar coater, the coating amount is controlled according to the conventional process for this functional layer, and drying is performed under corresponding drying conditions, so as to obtain the multi-layer coated packaging paperboard; Then, the combined method of accelerated aging and surface analysis is used to test the small molecule migration rate, which is specifically as follows: first, the obtained multi-layer coated packaging paperboard sample is placed in an oven at 60°C for accelerated aging for 72 h to accelerate the upward migration of residual small molecules in the lower layer. After aging, X-ray photoelectron spectroscopy (XPS) is used to analyze the chemical composition of the coating surface. First, element S, element Si or element N is selected as the characteristic labeling element; wherein: element S corresponds to the residue derived from the sulfonate surfactant (sodium dodecyl sulfate) in the water-based ink or coating in the migratory substance; element Si corresponds to the residue derived from the polyether-modified silicone oil defoamer in the migratory substance; element N corresponds to the residue derived from the amine pH regulator (such as triethanolamine) in the migratory substance. During the test, first, the characteristic labeling element with a significant content in the lower coating is determined by XPS full-spectrum scanning, and the characteristic labeling element with the highest signal intensity is selected as the target labeling element for quantitative analysis. Then, XPS is used to obtain the atomic percentage (at.%) of each element on the coating surface of the multi-layer coated packaging paperboard, and the atomic percentage of the target labeling element is used as the quantitative index of "small molecule migration amount". The higher the atomic percentage, the more small molecules migrate to the surface. The XPS quantification adopts the relative sensitivity factor method, and the calculation formula is as follows: C i (at.%)=(I i / RSF i ) / Σ(I j / RSF j )×100%; wherein, C i is the atomic percentage of the target labeling element, I i is the peak area of the target labeling element, RSF i is the relative sensitivity factor of the target labeling element, RSF j is the relative sensitivity factor of element j, which is provided by the sensitivity factor database built in the quantitative analysis software supporting the XPS instrument; Then, the migration inhibition rate of the target labeling element is calculated according to the following formula, and the calculation formula is as follows: Migration inhibition rate=(C 特征对照 -C 特征测试 ) / C 特征对照 ×100%; Among them, C-characteristic control is the atomic percentage of target marker elements on the surface of the control sample without interface isolation coating, and C-characteristic test is the atomic percentage of target marker elements on the surface of the test sample with interface isolation coating.

[0044] (3) Surface energy: First, an interfacial isolation coating is prepared. The specific preparation method includes: taking the coating composition and applying it to the release film using a wire rod coater. The coating amount (dry weight) is 2 g / m. 2 The surface energy of the interface isolation coating was obtained by drying at 90°C for 3 min. The surface energy of the interface isolation coating was then determined by the contact angle method. The test was carried out in accordance with the international standard ISO 19403-2:2024, with water and diiodomethane as test liquids. The contact angle of the interface isolation coating surface was measured, and the surface energy was calculated by the Owens-Wendt method.

[0045] The coating compositions provided in Examples 1-6 and Comparative Examples 1-4 were tested according to the above test methods, and the test results are shown in Table 2. Table 2 According to the data in Table 2: The coating compositions obtained in Examples 1-6 have a pH value of 6.4-6.9, which is close to neutral. The surface energy of the coating is 39.8-42.3 mN / m, which is suitable. After being further processed into multilayer coated packaging paperboard, the small molecule migration inhibition rate is not less than 78.5%.

[0046] Compared with Example 1, the surface energy of the coating compositions provided in Comparative Examples 1 to 4 after coating is either too high or too low, and the inhibition rate of small molecule migration is low after further processing into multilayer coated packaging paperboard.

[0047] The above description is only a specific embodiment of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A coating composition, characterized in that, The coating composition comprises water and solid components, wherein the solid components, based on a total mass of 100%, include: Polyvinyl alcohol 30-50%; Nonionic polyurethane dispersion 20-40%; 10-30% of the filler is sheet-like nanofiller.

2. The coating composition according to claim 1, characterized in that, The solid content of the coating composition is 15-25%.

3. The coating composition according to claim 1 or 2, characterized in that, The degree of alcoholysis of the polyvinyl alcohol is 84-90%, preferably 86-89%; And / or, the nanofiller comprises flaky kaolin; And / or, the aspect ratio of the nanofiller is ≥50; And / or, the D of the nanofiller 50 Flake diameter ≤ 0.5 μm.

4. The coating composition according to any one of claims 1 to 3, characterized in that, The coating composition also includes a leveling agent; Preferably, the total mass of the solid components is 100%, and the mass percentage of the leveling agent is 1-5%. Preferably, the leveling agent comprises an acetylenic diol nonionic surfactant.

5. A method for preparing a coating composition according to any one of claims 1 to 4, characterized in that, The preparation method includes: mixing solid components evenly in water, filtering, and obtaining the coating composition.

6. An interface isolation coating, characterized in that, The interface isolation coating is formed by leveling and drying the coating composition as described in any one of claims 1 to 4.

7. The application of the interface isolation coating as described in claim 6 in multilayer coated packaging paperboard.

8. A multi-layer coated packaging paperboard, characterized in that, The multilayer coated packaging paperboard includes stacked paperboard, the interface isolation coating as described in claim 6, and an upper functional layer.

9. The multi-layer coated packaging paperboard according to claim 8, characterized in that, A lower functional layer is also included between the cardboard and the interface isolation coating; And / or, the areal density of the interface isolation coating is 1~3 g / m³. 2 .

10. A method for preparing the multilayer coated packaging paperboard as described in claim 8 or 9, characterized in that, The preparation method includes: coating the surface of the paperboard with the coating composition as described in any one of claims 1 to 4, drying it, and then coating it with an upper functional layer material to obtain the multilayer coated packaging paperboard.

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