Liquid food packaging paper and preparation process thereof

Abstract

The invention belongs to the technical field of packaging paper, and particularly relates to liquid food packaging paper and a preparation technology thereof.The preparation technology comprises the steps that 1, coating liquid is prepared, specifically, the coating liquid is prepared from, by weight, 30-50 parts of waterborne polyurethane emulsion, 10-25 parts of waterborne acrylic emulsion, 10-20 parts of modified composite filler, 3-6 parts of oil hydrophobic auxiliaries and a proper amount of water; uniformly mixing the raw materials of the coating liquid to obtain the coating liquid; (2) base paper is coated with the coating liquid, and the liquid food packaging paper is obtained.The prepared liquid food packaging paper has the advantages of being high in structural strength, good in barrier property and uniform in coating.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of packaging paper, and particularly relates to a liquid food packaging paper and a preparation process thereof. BACKGROUND

[0002] Liquid food packaging paper is a packaging material specially used for containing or wrapping liquid food, such as milk, fruit juice, soy milk, soup, seasoning liquid, etc. It generally uses paper as a base material, and through coating or laminating other materials such as plastic, aluminum foil, etc. to achieve the performance requirements of waterproof, oil-proof, heat-resistant, sealing and oxygen barrier. Common liquid food packaging papers include PE-coated paper, aluminum-plastic composite paper, PLA-coated paper, etc. Among them, the coated liquid food packaging paper refers to coating one or more functional coatings on the surface of the paper by physical or chemical methods, such as PE, PLA, wax, acrylic emulsion, SiO2 nano coating, etc. to enhance its waterproof, oil-proof, barrier and heat-seal performance, so that it is suitable for the packaging of liquid food.

[0003] The structure of the coated packaging paper is generally paper base + functional coating layer, and the processing methods mainly include extrusion coating, knife coating, rod coating, roller coating, gravure printing, spraying, etc. It is mainly suitable for the packaging of liquid or semi-liquid food such as cold drinks, short-keeping liquids, environmentally friendly packaging, take-out cups / bags / boxes, etc. Coated liquid food packaging paper is increasingly widely used in cold drinks, freshly squeezed fruit juice, environmentally friendly food packaging, etc. due to its light and thin structure, diverse functions and environmentally friendly characteristics. Although its comprehensive barrier property is not as good as that of traditional aluminum-plastic composite materials, it can still meet the packaging needs of most liquid foods through the combination of multifunctional coatings, especially for the green packaging transformation trend. However, there are still some obvious defects and technical limitations in the coated packaging paper, which are as follows: 1. Limited barrier performance: The barrier performance of the coating layer of the coated packaging paper, such as PE, PLA, and acrylic coating, is much lower than that of aluminum foil or multi-layer composite film material. It is limited for the application of food with long shelf life, such as room temperature fruit juice and milk. 2. Low structural strength: Compared with multi-layer composite film, the coated paper has limited puncture resistance, tear resistance and folding loss resistance. It is more prone to damage during transportation or filling, especially in a wet state. If the coating layer is not complete, the paper will swell, delaminate or soften, leading to packaging rupture. 3. Easy to produce coating defects: The process requires high requirements and is prone to coating defects. If there are pinholes, uneven coating or mechanical damage in the coating layer, it will cause liquid penetration and paper failure. Therefore, the waterproof effect is highly dependent on the coating integrity.

[0004] Therefore, it is one of urgent technical problems for those skilled in the art to provide a liquid food packaging paper with high barrier property, structural strength, stable coating quality and effectively reduced coating defects and a preparation process thereof, which has very important significance for expanding the application field of the coated liquid food packaging paper and improving its market share. SUMMARY

[0005] The present application aims to solve the above technical problems and provide a liquid food packaging paper and a preparation process thereof, so as to improve the barrier property, structural strength and coating quality of the liquid food packaging paper.

[0006] Therefore, the present application provides a preparation process of a liquid food packaging paper, which comprises the following steps: (1) preparing a coating liquid, the coating liquid comprises, by weight, 30-50 parts of a water-based polyurethane emulsion, 10-25 parts of a water-based acrylic emulsion, 10-20 parts of a modified composite filler, 3-6 parts of an oil-based hydrophobic additive and an appropriate amount of water, the raw materials of the coating liquid are uniformly mixed to obtain the coating liquid; (2) coating the coating liquid on a base paper to obtain the liquid food packaging paper.

[0007] Further, the modified composite filler is a mixture of modified sheet-like montmorillonite and nano-silicon dioxide.

[0008] Further, the sheet-like montmorillonite has a sheet thickness of 0.7-4 nm and a particle size of 200-1000 nm, and the nano-silicon dioxide has a particle size of 20-80 nm.

[0009] Further, in the modified composite filler, the weight ratio of the sheet-like montmorillonite to the nano-silicon dioxide is (1-2):1, and the particle size of the sheet-like montmorillonite is 5-20 times the particle size of the nano-silicon dioxide.

[0010] Further, the preparation process of the modified composite filler is as follows: first, 80-100 parts by weight of water is taken, then 3-7 wt% of ethanol or isopropyl alcohol is added to the water, and low-speed stirring is performed at a speed of 100-300 rpm for 2-5 min, then 5-10 parts by weight of sheet-like montmorillonite and 0.5-2 parts by weight of a silane coupling agent are dispersed into the water in batches to prepare a water dispersion of the sheet-like montmorillonite, and a pH adjusting liquid is slowly added dropwise to adjust the pH of the water dispersion to 8-9; After heating, under the condition of 55-65℃ and 100-300rpm, the reaction is carried out for 1-2h, then the nano-silica and 20-40wt% polyacrylic acid solution with 5-8wt% concentration are added, and the reaction is continued under the condition of 55-65℃ and 100-300rpm for 1-2h, after filtration and drying, the pretreated composite filler is obtained; Then the composite filler powder is dispersed into the ethanol aqueous solution to prepare a dispersion liquid with 5-10wt% composite filler content, then 4-7wt% acrylic acid-2-ethylhexyl ester, 0.1-0.3wt% initiator and 0.05-0.1wt% crosslinking agent are added, after stirring, the reaction is carried out under the protection of inert atmosphere at 65-75℃ for 1-2.5h, after the reaction is completed, after filtration, water washing and drying, the modified composite filler is obtained.

[0011] Further, the oil hydrophobic auxiliary agent is a mixture of silicon oil synthetic oil and natural oil.

[0012] Further, the oil hydrophobic auxiliary agent is a mixture of dimethyl silicone oil and vegetable oil, and the mass ratio of the dimethyl silicone oil and the vegetable oil is (0.5-1):2.

[0013] Further, the solid content of the water-based polyurethane emulsion is 30-40wt%, the viscosity at 25℃ is <500mPa·s, the glass transition temperature (Tg) is -10℃-20℃, and the average particle size of the water-based polyurethane emulsion is <200nm.

[0014] Further, the solid content of the water-based acrylic emulsion is 40-55wt%, the viscosity at 25℃ is <800mPa·s, the glass transition temperature (Tg) is -10℃-30℃, and the average particle size of the water-based acrylic emulsion is <200nm.

[0015] In addition, the application also provides a liquid food packaging paper prepared by the preparation process of the liquid food packaging paper.

[0016] The liquid food packaging paper prepared by the application has the advantages of high structural strength, good barrier performance and uniform coating. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic diagram of the action principle of the composite filler. DETAILED DESCRIPTION

[0018] With reference to the drawings, the technical solutions in the embodiments of the present application will be clearly described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art belong to the scope of protection of the present application.

[0019] In the description of the present application, it should be noted that the terms used herein are only intended to describe specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. For the convenience of description, the technologies, methods and devices known to those skilled in the related art can not be discussed in detail, but in appropriate cases, the technologies, methods and devices should be considered as part of the authorized description. In all examples shown and discussed herein, any specific value should be interpreted as merely exemplary, and not as a limitation. Therefore, other examples of exemplary embodiments can have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0020] It should be noted that in the present application, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such process, method, article or device. Without more limitations, the element defined by the sentence "includes a" does not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, but can also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method can be performed in an order different from the described order, and various steps can also be added, omitted or combined. In addition, the features described with reference to certain examples can be combined in other examples.

[0021] A preparation process of a liquid food packaging paper, comprising the steps of: (1) preparing a coating liquid: the coating liquid comprises, by weight parts, 30-50 parts of a water-based polyurethane emulsion, 10-25 parts of a water-based acrylic emulsion, 10-20 parts of a modified composite filler, 3-6 parts of an oil-based hydrophobic auxiliary agent, and an appropriate amount of water, the raw materials of the coating liquid are uniformly mixed to obtain the coating liquid; (2) coating the coating liquid on the base paper to obtain the liquid food packaging paper.

[0022] Preferably, the solid content of the aqueous polyurethane emulsion is 30-40wt%; the viscosity at 25℃ is <500mPa·s, so as to facilitate blending with other components and adapt to high-speed coating; the glass transition temperature (Tg) is -10℃-20℃, so as to ensure the flexibility and low-temperature non-brittle cracking of the coated film after the coating liquid is formed into a film.

[0023] Preferably, the average particle size of the aqueous polyurethane emulsion is <200nm.

[0024] Preferably, the solid content of the aqueous acrylic emulsion is 40-55wt%; the viscosity at 25℃ is <800mPa·s; the glass transition temperature (Tg) is -10℃-30℃, so as to ensure the flexibility and low-temperature non-brittle cracking of the coated film after the coating liquid is formed into a film.

[0025] Preferably, the average particle size of the aqueous acrylic emulsion is <200nm, and more preferably, the average particle size of the aqueous acrylic emulsion is 80-150nm.

[0026] Preferably, the pH of the aqueous polyurethane emulsion is 6.5-8.5, and the pH of the aqueous acrylic emulsion is 7-8.5.

[0027] In the preparation process of the liquid food packaging paper described in the present application, a dense and continuous coating film is formed on the surface of the paper by using the aqueous polyurethane emulsion and the aqueous acrylic emulsion as the core film-forming and functional building material, effectively sealing the pores of the paper, improving the permeation resistance of the packaging paper to water, oil, liquid food and the like, and ensuring the liquid resistance and cleanliness of the packaging material under the condition of liquid contact. At the same time, the soft segment (such as polyether, polyester) and hard segment (such as isocyanate structure) in the aqueous polyurethane emulsion chain segment have good flexibility, elasticity and tear resistance after film formation; the aqueous acrylic emulsion has high tensile strength and wear resistance, which can enhance the overall mechanical properties of the coating layer, and the combination of the two can balance the flexibility and rigid support of the coating layer, improve the anti-cracking, anti-brittle and folding resistance of the coating layer, and is particularly suitable for food packaging paper in dynamic stress environments such as refrigeration and curling.

[0028] In addition, the acrylic emulsion contains polar functional groups such as carboxyl and hydroxyl groups, which can form hydrogen bonds or electrostatic interactions with the paper fibers, and the polyurethane emulsion mainly contains hydrophilic segments, which can also enhance the interfacial bonding force with the paper base, and the combination of the two can help to form a stable coating layer with high bonding strength and low peeling risk with the paper base.

[0029] Further, the modified composite filler is a mixture of modified sheet-like montmorillonite and nano-silicon dioxide.

[0030] Preferably, the sheet-like montmorillonite has a sheet thickness of 0.7-4nm, and the sheet-like montmorillonite has a particle size of 200-1000nm.

[0031] Preferably, the particle size of the nano-silica is 20-80 nm.

[0032] More preferably, the nano-silica is spherical or nearly spherical in shape.

[0033] More preferably, in the present invention, the particle size of the selected flaky montmorillonite is 5 to 20 times the particle size of the nano-silicon dioxide.

[0034] Preferably, in the modified composite filler, the weight ratio of the flaky montmorillonite to the nano-silica is (1-2):1.

[0035] In the coating formed by the coating liquid of the present invention, the spatial nesting and staggered stacking between the large-sized flaky montmorillonite and the small-sized spherical silica can form a "nano-composite multi-layer barrier structure" with high density and barrier performance. Figure 1 As shown in the figure, in this structure, the flaky montmorillonite tends to be oriented along the surface of the paper during the coating process, like layers of bricks and tiles, and the nano-silica fills the gaps or edge areas between the layers, similar to mortar or spacer fillers. This staggered structure is similar to a "nano-composite multi-layer barrier", which can significantly improve the density, liquid permeability, gas barrier properties and mechanical strength of the coating, thereby inhibiting the penetration of liquids or greases, slowing the transmission rate of oxygen and water vapor, and forming a functional barrier while ensuring the flexibility of the paper.

[0036] As some examples of the present invention, in order to obtain flaky montmorillonite that meets the above-mentioned size requirements, before preparing the modified composite filler, the montmorillonite flakes can be dispersed using ultrasound or a high shear machine, or the montmorillonite can be intercalated using an intercalating agent to ensure that the size of the flaky montmorillonite used meets the requirements.

[0037] Furthermore, the preparation process of the modified composite filler is as follows: First, 80 to 100 parts by weight of water are taken, and then 3 to 7 wt% of ethanol or isopropanol is added to the water, and the mixture is stirred at a low speed of 100 to 300 rpm for 2 to 5 minutes. Then, 5 to 10 parts by weight of flaky montmorillonite and 0.5 to 2 parts by weight of a silane coupling agent are dispersed in the water in batches to prepare an aqueous dispersion of the flaky montmorillonite, and a pH adjusting solution is slowly added dropwise to adjust the pH of the aqueous dispersion to 8 to 9; Then, heating and reacting at a temperature of 55-65° C. and a rotation speed of 100-300 rpm for 1-2 hours, adding the formulated amount of nano-silica and 20-40 parts by weight of a polyacrylic acid solution with a concentration of 5-8wt%, and continuing to react at a temperature of 55-65° C. and a rotation speed of 100-300 rpm for 1-2 hours, filtering and drying to obtain a pretreated composite filler; Then the composite filler powder is dispersed into an aqueous ethanol solution to prepare a dispersion liquid with a composite filler content of 5-10 wt%, and then 4-7 parts by weight of 2-ethylhexyl acrylate, 0.1-0.3 parts by weight of an initiator, and 0.05-0.1 parts by weight of a crosslinking agent are added, stirred and uniformly mixed, and then reacted at 65-75°C under inert atmosphere protection for 1-2.5 hours. After the reaction is completed, the modified composite filler is obtained after filtration, water washing, and drying.

[0038] As some examples of the present application, the pH adjusting liquid is a sodium hydroxide or ammonia solution with a concentration of 0.1-0.5 mol / L.

[0039] As some examples of the present application, the initiator is potassium persulfate, benzoyl peroxide, ammonium persulfate, etc.

[0040] As some examples of the present application, the crosslinking agent is N,N'-methylenebisacrylamide, diethylenetriamine pentaacetic acid dipropenamide, acryloyloxyethyl methacrylate, etc.

[0041] It is known that montmorillonite is a typical layered silicate, and the surface of its sheet layer has certain hydrophilic and hydrophobic regions, and there is weak van der Waals force or ionic bond between the layers. Directly adding it into water can easily cause agglomeration and flocculation. In the preparation process of the modified composite filler described in the present application, the sheet-shaped montmorillonite is dispersed into a mixture of ethanol or isopropanol and water, which can significantly reduce the surface tension of the system (tests have found that the addition of ethanol or isopropanol can reduce the surface tension of water from about 72 mN / m to about 30-40 mN / m) by using ethanol or isopropanol as a polar solvent with low surface tension. After mixing with water, the polar solvent molecules of the alcohol-containing solution can easily enter the interlayer, effectively weaken the interlayer adsorption force, and promote the separation of the sheet layer. This can more fully wet the surface of the sheet-shaped montmorillonite, form a more uniform and stable initial dispersion system with water, prevent agglomeration caused by local dewetting, and further help the single-layer / few-layer sheet-shaped structure after peeling to form an arrangement structure that is oriented along the surface direction of the paper in the coating layer, thereby ultimately improving the uniformity of the coating liquid and better and more uniformly forming the above-mentioned "nanocomposite multi-layer barrier structure" in the coating layer.

[0042] Further, in the process of preparing the modified composite filler, the shear force can be controlled by low-speed stirring reaction to avoid particle breakage and agglomeration. For structure-sensitive materials such as flaky montmorillonite and nano-silicon dioxide, the already exfoliated montmorillonite layers can be prevented from being broken by shear, and the nano-particles can be prevented from being agglomerated into clusters due to high shear, which affects the dispersion quality. At the same time, the uniform reaction is ensured, the modification efficiency is improved, and the modified filler still maintains the original morphology structure and particle size advantage. More importantly, the low shear environment is conducive to the directional flattening of flaky montmorillonite during stirring and heating, which helps to build a pre-arrangement system with "size complementarity + directional arrangement", and provides a basis for the subsequent construction of staggered structure.

[0043] Further, in the process of preparing the modified composite filler, the very important functionalization can be achieved by adding polyacrylic acid solution. Specifically, polyacrylic acid is a linear polymer with a large number of carboxyl groups (-COOH) or sodium salt form (-COO - On the one hand, under alkaline conditions (pH 8-9), it will ionize to form negative charges, which can prevent particle agglomeration through electrostatic repulsion and steric hindrance. On the other hand, polyacrylic acid molecules can be adsorbed on the surface of flaky montmorillonite and nano-silicon dioxide to form a stable coating layer, thereby improving the dispersion uniformity and storage stability of the whole system, which is particularly important for subsequent blending with coating emulsion and forming a uniform coating. At the same time, the carboxyl groups on the polyacrylic acid segment can form hydrogen bonds, weak coordination bonds, or participate in subsequent graft copolymerization with the hydroxyl groups on the surface of SiO2 and the interlayer structure of montmorillonite, and then integrate the inorganic particles into an organic-inorganic network structure, thereby improving the structural stability of the modified composite filler. In addition, the commonly used adhesives in coating liquids, such as water-based polyurethane and acrylic emulsion, are hydrophilic or anionic emulsion. The introduction of polyacrylic acid makes the surface of the composite filler have hydrophilic and polar functional groups, which can effectively enhance the adhesion between the filler and the emulsion matrix, and prevent the filler from migrating, agglomerating or precipitating due to poor compatibility during coating or drying. Therefore, the introduction of polyacrylic acid solution in the preparation process of the composite filler has the functions of dispersion stability, surface modification and structure synergy, which not only improves the water dispersion stability of nano-particles and prevents agglomeration, but also promotes the organic-inorganic interface bonding by forming hydrogen bonds or complex structures between carboxyl groups and inorganic components, thereby building a composite filler with excellent distribution, flexibility and interface affinity, which provides key support for the denseness, liquid resistance and film stability of the subsequent coating.

[0044] Furthermore, in the process of preparing the modified composite filler, a flexible coating layer can be formed on the surface of the filler by introducing 2-ethylhexyl acrylate and performing polymerization reaction under the action of initiator and crosslinking agent, which plays a "buffer layer" role and helps to improve the compatibility of the filler with the organic matrix and the flexibility and anti-brittle performance of the overall coating.

[0045] In addition, the long branched alkyl group in the polymer main chain structure of 2-ethylhexyl acrylate makes it have good repellency to water and oil, which can significantly improve the liquid penetration resistance, water resistance, oil resistance and moisture and fog resistance of the composite filler, and further improve the barrier property of the liquid food packaging paper.

[0046] In addition, compared with rigid monomers, 2-ethylhexyl acrylate is a hydrophobic soft monomer, and the polymer thereof has a low glass transition temperature (Tg≈-60℃), good flexibility and is not easy to be brittle, so that the modified composite filler can be deformed cooperatively with the flexible matrix in the coating, buffer stress concentration, and significantly improve the mechanical stability and low-temperature flexibility of the coating under folding, winding, low-temperature storage and other working conditions.

[0047] Further, the oil hydrophobic aid is an aid derived from natural oil or synthetic oil, and the main function is to improve the hydrophobicity of the material surface, Preferably, the oil hydrophobic aid is a mixture of silicone oil synthetic oil and natural oil.

[0048] As some examples of the present application, the silicone oil synthetic oil can be dimethyl silicone oil, hydroxy silicone oil, amino silicone oil, quaternary ammonium silicone oil, etc., and preferably dimethyl silicone oil.

[0049] As some examples of the present application, the natural oil can be vegetable oil, such as rapeseed oil, peanut oil, soybean oil, palm oil, etc., or animal fat.

[0050] Preferably, the natural oil is vegetable oil.

[0051] More preferably, the mass ratio of dimethyl silicone oil to natural oil is (0.5-1):2.

[0052] Preferably, the content of oleic acid in the natural oil is 60-80wt%.

[0053] In the coating liquid of the present application, a small amount of dimethyl silicone oil and vegetable oil can be added to construct a low surface energy barrier layer on the surface of the coating by the synergistic effect of the two, which can significantly improve the anti-permeation and anti-adsorption ability to water, fruit juice, dairy products and other liquids.

[0054] In addition, the dimethyl silicone oil molecular chain is soft and smooth, which can act as an internal lubricant during film formation, making the coating surface smoother and more uniform, improving the coating quality and appearance.

[0055] Further, the plant oil selected by the present application has an oleic acid content of 60-80 wt%, at this time, the plant oil shows good hydrophobicity, which is helpful to form a continuous and soft hydrophobic film in the coating, thereby improving the waterproof and oil-proof performance, meanwhile, the presence of oleic acid enhances the lubricity and softness of the coating, which is beneficial to the processing performance and user experience of the packaging paper. More importantly, the double bond structure of oleic acid enables the plant oil to have certain low-temperature fluidity and softening effect, which is helpful to keep the coating flexible and not easy to crack in cold storage or low-temperature environment, and the present application limits the content of oleic acid to 60-80 wt%, so as to balance the flexibility and strength, and meet the demand of liquid food packaging for soft and durable coating.

[0056] As some examples of the present application, the coating liquid further comprises 0.3-0.5 parts of defoaming agent and 0.5-2 parts by weight of dispersing agent.

[0057] Further, the concentration of the prepared coating liquid of the present application is 25-35 wt%, and the dry coating amount of the coating liquid on the base paper is 3-8 g / m 2 .

[0058] As some examples of the present application, the coating method of the coating liquid can be extrusion film coating, knife coating, rod coating, roller coating, gravure printing, spraying, etc.

[0059] The liquid food packaging paper and the preparation process thereof according to the present application are illustrated by specific examples as follows: Example 1 Preparation of modified composite filler: First, 80 parts by weight of water was taken, then 3 wt% of ethanol was added to the water, and low-speed stirring was carried out at a speed of 120 r / min for 3 min, then 5 parts by weight of flaky montmorillonite and 0.5 parts by weight of silane coupling agent were dispersed into the water in batches to prepare a water dispersion of flaky montmorillonite, and the pH of the water dispersion was adjusted to 8 by slowly adding a pH adjusting solution; Then, heating was carried out, and after reaction for 2 h under the condition of temperature 55℃ and low-speed stirring at a speed of 100 r / min, 5 parts by weight of nano-silicon dioxide and 20 parts by weight of polyacrylic acid solution with a concentration of 5 wt% were added, and the reaction was continued for 2 h under the condition of temperature 55℃ and low-speed stirring at a speed of 100 r / min, then after filtration and drying, the pretreated composite filler was obtained; Then, the composite filler powder was dispersed into the ethanol aqueous solution to prepare a dispersion liquid with a composite filler content of 5 wt%, then 4 parts by weight of acrylic acid-2-ethylhexyl ester, 0.1 parts by weight of initiator and 0.05 parts by weight of crosslinking agent were added, and after stirring, the reaction was carried out under the protection of inert atmosphere at 65℃ for 2.5 h, after the reaction was completed, the modified composite filler was obtained after filtration, water washing and drying.

[0060] Example 2 Preparation of modified composite filler: First, 100 parts by weight of water was taken, then 7wt% of isopropyl alcohol was added to the water, and stirred at a low speed of 300rpm for 2min, then 10 parts by weight of flaky montmorillonite and 2 parts by weight of silane coupling agent were dispersed into the water in batches to prepare a water dispersion of flaky montmorillonite, and the pH of the water dispersion was adjusted to 9 by slowly adding a pH adjusting solution; Then heated, after 1h of reaction at a temperature of 65℃ and a low speed of 300rpm, 5 parts by weight of nano-silica and 40 parts by weight of a polyacrylic acid solution with a concentration of 8wt% were added, and the reaction was continued at a temperature of 65℃ and a low speed of 300rpm for 1h, then the composite filler was obtained after filtration and drying; Then the composite filler powder was dispersed in an ethanol aqueous solution to prepare a dispersion with a composite filler content of 10wt%, then 7 parts by weight of 2-ethylhexyl acrylate, 0.3 parts by weight of an initiator, and 0.1 parts by weight of a crosslinking agent were added, and after stirring, the reaction was carried out at 75℃ for 1.5h under inert atmosphere protection, and after the reaction was completed, the modified composite filler was obtained after filtration, water washing, and drying.

[0061] Examples 3-6 Preparation of coating liquid sample: The raw materials were prepared according to the weight ratio shown in Table 1 below, then all the raw materials were mixed uniformly to prepare a coating liquid with a concentration of 30wt%.

[0062] The water-based polyurethane emulsion used has a solid content of 32wt%, a viscosity of 485mPa·s at 25℃, and an average particle size of 173nm; The water-based acrylic emulsion used has a solid content of 45wt%, a viscosity of 640mPa·s at 25℃, and an average particle size of 125nm; The modified composite filler used in Examples 3 and 4 is the modified composite filler prepared in Example 1 above, and the modified composite filler used in Examples 5 and 6 is the modified composite filler prepared in Example 2 above; The oil-based hydrophobic agent is a mixture of dimethyl silicone oil and vegetable oil, the mass ratio of the dimethyl silicone oil and the vegetable oil is 1:2, and the content of oleic acid in the vegetable oil is 76wt%; The defoaming agent is BYK-024, and the dispersant is TEGO Dispers 755.

[0063] Examples 7-10 Preparation of liquid food packaging paper: The coating liquid was coated on the base paper according to the requirements of Table 2 below to obtain a liquid food packaging paper, wherein the base paper was a kraft paper available on the market: Comparative Example 1 Preparation of the liquid food packaging paper: The difference between it and the above-mentioned Example 9 is only that the mixture of the unmodified sheet-shaped montmorillonite and the nanosilica was directly added in the coating liquid instead of the modified composite filler in Example 9.

[0064] Comparative Example 2 Preparation of the liquid food packaging paper: The difference between it and the above-mentioned Example 9 is only that the mixture of the unmodified sheet-shaped montmorillonite and the nanosilica was directly added in the coating liquid instead of the modified composite filler in Example 9.

[0065] Comparative Example 3 Preparation of the liquid food packaging paper: The difference between it and the above-mentioned Example 9 is only that the oil hydrophobic aid added in the coating liquid only contains dimethyl silicone oil, and does not contain vegetable oil.

[0066] Comparative Example 4 Preparation of the liquid food packaging paper: The difference between it and the above-mentioned Example 9 is only that the oil hydrophobic aid added in the coating liquid contains a lower content of oleic acid in the vegetable oil, only 18wt%.

[0067] Performance detection: The liquid food packaging papers prepared in the above-mentioned Examples 7-10 and Comparative Examples 1-4 were subjected to performance detection, and at the same time, the base paper of kraft paper without coating the coating liquid was subjected to performance detection as a blank control sample, and the detection results were as follows: Among them, the tensile strength test was carried out according to GB / T12914-2018; the water vapor transmission rate test was carried out according to GB / T22921-2008, the Cobb 60 value test was carried out according to ISO 535:1991 and TAPPI T441 om-09, and the oil resistance grade test was carried out according to TAPPI T 559 cm-02.

[0068] The above describes the embodiments of the present application, and in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other, the present application is not limited to the above-mentioned specific embodiments, the above-mentioned specific embodiments are only illustrative, but not limited, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the scope of the present application and the protection scope of the claims, all of which belong to the protection of the present application.

Claims

1. A process for preparing liquid food packaging paper, characterized in that: Including steps: (1) Preparing a coating liquid: The coating liquid comprises, by weight, 30 to 50 parts of an aqueous polyurethane emulsion, 10 to 25 parts of an aqueous acrylic emulsion, 10 to 20 parts of a modified composite filler, 3 to 6 parts of an oil-based hydrophobic additive, and an appropriate amount of water. The raw materials of the coating liquid are uniformly mixed to obtain a coating liquid; (2) Apply the coating liquid on the base paper to obtain liquid food packaging paper.

2. The process for preparing liquid food packaging paper according to claim 1, characterized in that: The modified composite filler is a mixture of modified flaky montmorillonite and nano silicon dioxide.

3. The process for preparing liquid food packaging paper according to claim 2, characterized in that: The thickness of the flaky montmorillonite is 0.7-4 nm, the particle size of the flaky montmorillonite is 200-1000 nm; and the particle size of the nano-silicon dioxide is 20-80 nm.

4. The process for preparing liquid food packaging paper according to claim 3, characterized in that: In the modified composite filler, the weight ratio of the flaky montmorillonite to the nano-silicon dioxide is (1-2):1, and the particle size of the flaky montmorillonite is 5-20 times that of the nano-silicon dioxide.

5. The process for preparing liquid food packaging paper according to claim 1, 2, 3 or 4, characterized in that: The preparation process of the modified composite filler is as follows: First, 80 to 100 parts by weight of water are taken, and then 3 to 7 wt% of ethanol or isopropanol is added to the water, and the mixture is stirred at a low speed of 100 to 300 rpm for 2 to 5 minutes. Then, 5 to 10 parts by weight of flaky montmorillonite and 0.5 to 2 parts by weight of a silane coupling agent are dispersed in the water in batches to prepare an aqueous dispersion of the flaky montmorillonite, and a pH adjusting solution is slowly added dropwise to adjust the pH of the aqueous dispersion to 8 to 9; Then, heating and reacting at a temperature of 55-65° C. and a rotation speed of 100-300 rpm for 1-2 hours, adding the formulated amount of nano-silica and 20-40 parts by weight of a polyacrylic acid solution with a concentration of 5-8wt%, and continuing to react at a temperature of 55-65° C. and a rotation speed of 100-300 rpm for 1-2 hours, filtering and drying to obtain a pretreated composite filler; The composite filler powder is then dispersed in an ethanol aqueous solution to prepare a dispersion with a composite filler content of 5-10 wt%, and then 4-7 parts by weight of 2-ethylhexyl acrylate, 0.1-0.3 parts by weight of an initiator, and 0.05-0.1 parts by weight of a cross-linking agent are added. After stirring, the mixture is reacted at 65-75° C. under an inert atmosphere for 1-2.5 hours. After the reaction is completed, the mixture is filtered, washed with water, and dried to obtain a modified composite filler.

6. The process for preparing liquid food packaging paper according to claim 1, characterized in that: The oil hydrophobic additive is a mixture of silicone oil, synthetic oil and natural oil.

7. The process for preparing liquid food packaging paper according to claim 1 or 6, characterized in that: The oil hydrophobic additive is a mixture of dimethyl silicone oil and vegetable oil, and the mass ratio of the dimethyl silicone oil to the vegetable oil is (0.5~1):

2.

8. The process for preparing liquid food packaging paper according to claim 1, characterized in that: The solid content of the aqueous polyurethane emulsion is 30-40 wt %; the viscosity at 25° C. is less than 500 mPa·s, the glass transition temperature is -10° C. to 20° C., and the average particle size of the aqueous polyurethane emulsion is less than 200 nm.

9. The process for preparing liquid food packaging paper according to claim 1, characterized in that: The solid content of the aqueous acrylic emulsion is 40-55 wt %; the viscosity at 25° C. is less than 800 mPa·s, the glass transition temperature is -10° C. to 30° C., and the average particle size of the aqueous acrylic emulsion is less than 200 nm.

10. Liquid food packaging paper prepared according to the process for preparing liquid food packaging paper according to any one of claims 1 to 9.

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