Waterborne shellac-nanosilicon composite coating and preparation method thereof, packaging material

Abstract

This invention relates to the field of coatings, and particularly to a water-based shellac-nanosilica composite coating and its preparation method, as well as packaging materials. The preparation method of the water-based shellac-nanosilica composite coating provided by this invention involves mixing sodium carboxymethyl cellulose with water and heating to dissolve it, forming a gel; mixing dewaxed bleached shellac, water, and the gel obtained in step S1, heating, adding a pH adjuster to adjust the pH value to 7.5-8.5, and stirring while maintaining the temperature to obtain a shellac ammonium salt-based solution; mixing nano-silica sol and methyltrimethoxysilane, and adding an acidic catalyst to adjust the pH value to 5.0-6.0, stirring for pre-hydrolysis to obtain a pre-hydrolyzed solution; mixing the pre-hydrolyzed solution with a silane coupling agent to obtain an activated solution; mixing the shellac ammonium salt-based solution with the activated solution to obtain a hybrid solution, and then introducing additives to obtain the water-based shellac-nanosilica composite coating. This invention achieves complete water-based coating, effectively improving storage stability, oil resistance, and high-temperature water resistance.

Description

Technical Field

[0001] This invention relates to the field of coatings, and particularly to a water-based shellac-nanosilicon composite coating and its preparation method, as well as packaging materials. Background Technology

[0002] Shellac is a naturally derived resin with excellent film-forming properties, biocompatibility, and adhesion, making it widely used in food packaging, wood coatings, and pharmaceutical coatings. However, traditional shellac coatings often use ethanol as a solvent, posing safety hazards such as high emissions of volatile organic compounds and flammability / explosiveness. To address this issue, water-based shellac coatings have become a research hotspot, but they still face many technical bottlenecks in commercial applications, especially when used in food contact materials, where the requirements for water resistance, high-temperature resistance, and safety are even more stringent.

[0003] Patent application CN104705392A discloses a preservative fruit wax containing bleached shellac, its preparation method, and its application. This formulation is composed of the following components in the indicated mass percentages: bleached shellac 3%-20%, glycerin 1%-5%, sodium hydroxide 0.1%-2%, oleic acid 0.5%-5%, morpholine 0.2%-4%, ammonia 0.1%-5%, hydroxypropyl methylcellulose 0.2%-3%, and deionized water 62%-93%. However, this formulation has the following drawbacks: it contains the toxic substance morpholine, which does not meet the safety requirements for food contact materials; although it claims to prevent whitening after film formation, the formula uses hydroxypropyl methylcellulose (HPMC) as a thickener and glycerin as a plasticizer, both of which are strongly hydrophilic substances; while HPMC provides a thickening effect, it cannot form a hydrophobic network; glycerin is prone to hygroscopic migration, causing the coating to soften and whiten upon contact with water.

[0004] Patent application CN115160803A discloses a shellac-based ultraviolet shielding composite material and its preparation method. This method uses shellac as the matrix, high-concentration ammonia water (1.2~12.0 mol / L, 8~10 parts) as the solvent, polyethylene glycol (molecular weight 600~1000 g / mol) as the plasticizer, sodium oleate, potassium oleate, or polysorbates as compatibilizers, and nanocellulose as the reinforcing agent. However, the above method has the following drawbacks: The use of polyethylene glycol (PEG) as the plasticizer is problematic because PEG is a highly hydrophilic substance, which significantly reduces the water resistance of the coating and easily dissolves in water, leading to coating defects. Furthermore, nanocellulose is also hydrophilic, limiting the improvement in coating density and high-temperature resistance.

[0005] Patent application CN110194906A discloses an edible-grade shellac mixture and its preparation method. This method dissolves edible-grade shellac in propylene glycol to form a solution insoluble in water and oil, suitable for use in food-grade printing inks and other fields. However, the above method has the following drawbacks: it still contains organic solvents, failing to achieve complete water-based application; it is merely a physical dissolution system of shellac in propylene glycol, without introducing any crosslinking agents or inorganic reinforcing phases; after drying, the coating is simply a physical accumulation of shellac itself, with limited improvement in density and thermal stability; although it claims good water resistance, this resistance mainly stems from the insoluble nature of shellac itself, rather than chemical modification; and shellac still slowly absorbs water and softens upon contact with water, resulting in insufficient long-term water resistance.

[0006] Patent application CN120349731A discloses a weather-resistant bio-based conductive coating based on water-based palm wax / shellac and its preparation method. This method combines water-based palm wax emulsion and shellac ethanol solution, adding silver-coated copper powder / carbon nanofiber composite material to improve the coating's weather resistance, flexibility, and moisture barrier properties. Its technical effects include: reduced coating moisture absorption to 12% (ASTM D570 standard), elongation at break >50%, and water vapor transmission rate <10 g / m²·day. However, the above method also has the following drawbacks: it still contains organic solvents, failing to achieve complete water-based application; it is costly, limiting commercial application; and the shellac and palm wax are compounded in the system, with the shellac added in ethanol solution form, failing to fully utilize the potential of shellac as the main film-forming resin.

[0007] Patent CN113444451B discloses a food-grade superhydrophobic coating, whose main raw materials are stearic acid, shellac, and ethyl cellulose, prepared through physical blending. The coating exhibits good adhesion to the substrate and a water contact angle exceeding 150°. This technical solution uses all food-grade raw materials, ensuring high safety. However, its drawbacks are: the shellac molecular structure remains unchanged through physical blending, limiting the improvement in the coating's heat resistance; and the superhydrophobic properties primarily rely on the low surface energy characteristics of stearic acid, resulting in insufficient stability of the coating under high temperature and high humidity environments. Summary of the Invention

[0008] In view of this, the present invention provides a water-based shellac-nanosilica composite coating and its preparation method, as well as a packaging material. The present invention achieves complete water-based application and effectively improves storage stability, oil resistance, and high-temperature water resistance.

[0009] This invention provides a method for preparing an aqueous shellac-nanosilica composite coating, comprising the following steps:

[0010] S1. Mix sodium carboxymethyl cellulose with water, heat to dissolve, and form a gel.

[0011] S2. Mix the dewaxed bleached shellac, water and the resin solution obtained in step S1, heat, add pH adjuster to adjust the pH value to 7.5~8.5, keep warm and stir to obtain shellac ammonium salt base solution.

[0012] S3. Mix nano-silica sol and methyltrimethoxysilane, add an acidic catalyst to adjust the pH to 5.0~6.0, stir and pre-hydrolyze to obtain a pre-hydrolyzed solution;

[0013] S4. Mix the pre-hydrolyzed solution obtained in step S3 with the silane coupling agent to obtain the activation solution;

[0014] S5. Mix the shellac ammonium salt base solution obtained in step S2 with the activation solution obtained in step S4, and react to obtain a hybrid solution;

[0015] S6. Mix the hybrid liquid obtained in step S5 with the additive to obtain an aqueous shellac-nanosilicon composite coating.

[0016] Preferably, the amounts of materials used in each step are as follows:

[0017] Dewaxed and bleached shellac: 10-20 parts by weight;

[0018] Sodium carboxymethyl cellulose: 0.3~1.5 parts by weight;

[0019] Water: 55-70 parts by weight;

[0020] Nano silica sol: 5~15 parts by weight;

[0021] Methyltrimethoxysilane: 2-8 parts by weight;

[0022] Silane coupling agent: 0.5~2 parts by weight;

[0023] Additives: 0.4~0.8 parts by weight.

[0024] Preferably, in step S4, the silane coupling agent is KH-570 and / or KH-550.

[0025] Preferably, in step S1, the heating and melting temperature is 50~80℃.

[0026] Preferably, in step S2:

[0027] The pH adjuster is ammonia water;

[0028] The heating temperature is 60~80℃.

[0029] Preferably, in step S3:

[0030] The SiO2 particles in the nano-silica sol have a particle size of 5-40 nm and a SiO2 content of 10%-40%.

[0031] The acidic catalyst is acetic acid and / or phosphoric acid;

[0032] The stirring speed for the pre-hydrolysis is 500~1000 rpm, and the time is 30~60 min.

[0033] Preferably, in step S5:

[0034] The mixing temperature is 40~60℃;

[0035] The reaction is carried out at a temperature of 40-60°C for 3-5 hours.

[0036] Preferably, in step S6:

[0037] The additives include bactericides, leveling agents, and defoamers;

[0038] The mixing temperature is ≤40℃.

[0039] The present invention also provides an aqueous shellac-nanosilicon composite coating, which is prepared by the preparation method described in the above technical solution.

[0040] The present invention also provides a packaging material, comprising a substrate and a coating compounded on the surface of the substrate; wherein the coating is formed by the water-based shellac-nano-silicon composite coating described in the above technical solution.

[0041] The present invention provides a method for preparing a water-based shellac-nanosilica composite coating, comprising: mixing sodium carboxymethyl cellulose with water and heating to dissolve it to form a gel; then mixing dewaxed bleached shellac, water, and the gel obtained in step S1, heating, adding a pH adjuster to adjust the pH value to 7.5-8.5, and stirring while maintaining the temperature to obtain a shellac ammonium salt base solution; furthermore, mixing nano-silica sol and methyltrimethoxysilane, adding an acidic catalyst to adjust the pH value to 5.0-6.0, stirring and pre-hydrolyzing to obtain a pre-hydrolyzed solution; then mixing the pre-hydrolyzed solution with a silane coupling agent to obtain an activated solution; then mixing the shellac ammonium salt base solution with the activated solution to obtain a hybrid solution, and then introducing additives to obtain a water-based shellac-nanosilica composite coating. This invention achieves a comprehensive performance breakthrough by using MTMS and silica sol to construct a hydrophobic rigid framework, CMC-Na to provide rheological regulation and network enhancement, silane coupling agent to provide interfacial bridging, and shellac to provide a bio-based film-forming matrix. The synergistic effect of these four components results in a breakthrough in comprehensive performance that is "non-settling during storage and water and oil blocking in the coating film". This solves the long-standing technical pain points of existing water-based shellac coatings, such as poor water resistance, insufficient hardness, and easy settling during storage.

[0042] The test results show that the coating of the present invention does not show any sedimentation or stratification after 30 days of heat storage at 50℃, the Kit value reaches above 8, the contact angle is above 90°, and the boiling water resistance time reaches above 30 minutes, demonstrating excellent storage stability, oil resistance and high temperature water resistance. Detailed Implementation

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0044] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0045] As used herein, the term "and / or" includes any and all combinations of one or more of the related listed items.

[0046] In this document, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0047] In this article, when referring to units for data ranges, if the unit is only followed by the right endpoint, it means that the units for the left and right endpoints are the same. For example, 1000~1500rpm means that the units for the left endpoint "1000" and the right endpoint "1500" are both rpm.

[0048] [First Aspect] This invention provides a method for preparing an aqueous shellac-nanosilica composite coating, comprising the following steps:

[0049] S1. Mix sodium carboxymethyl cellulose with water, heat to dissolve, and form a gel.

[0050] S2. Mix the dewaxed bleached shellac, water and the resin solution obtained in step S1, heat, add pH adjuster to adjust the pH value to 7.5~8.5, keep warm and stir to obtain shellac ammonium salt base solution.

[0051] S3. Mix nano-silica sol and methyltrimethoxysilane, add an acidic catalyst to adjust the pH to 5.0~6.0, stir and pre-hydrolyze to obtain a pre-hydrolyzed solution;

[0052] S4. Mix the pre-hydrolyzed solution obtained in step S3 with the silane coupling agent to obtain the activation solution;

[0053] S5. Mix the shellac ammonium salt base solution obtained in step S2 with the activation solution obtained in step S4, and react to obtain a hybrid solution;

[0054] S6. Mix the hybrid liquid obtained in step S5 with the additive to obtain an aqueous shellac-nanosilicon composite coating.

[0055] In this invention, steps that are sequentially related are performed in that order, while steps that are not sequentially related have no special restrictions on their order. "Steps that are not sequentially related" refers to steps that do not necessarily have a sequential relationship. For example, steps S1 and S2: step S1 uses the transparent adhesive obtained in step S1, therefore step S1 must be performed before step S2 can be performed; that is, they are sequentially related, and in this case, they must be performed in that order. Similarly, steps S1 and S3, etc., are not sequentially related, therefore, their order has no special restrictions; the same applies to other steps, and further examples will not be provided.

[0056] Regarding step S1 :

[0057] S1 (CMC-Na pre-dissolved): Sodium carboxymethyl cellulose (CMC-Na) is mixed with water and heated to dissolve, forming a gel.

[0058] In this invention, the source of CMC-Na is not particularly limited; it can be a commercially available product or prepared according to methods known in the art.

[0059] In this invention, the water is preferably deionized water.

[0060] In this invention, the preferred heating and dissolving temperature is 50-80℃, specifically 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, and more preferably 60℃. In this invention, after heating to the target temperature, stirring is performed until complete dissolution. The preferred stirring speed is 1000-1500 rpm, specifically 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, and 1500 rpm. After the above treatment, a glue solution is obtained.

[0061] Regarding step S2 :

[0062] S2 (Preparation of shellac ammonium salt solution): Dewaxed and bleached shellac, water and the shellac solution obtained in step S1 are mixed, heated, and a pH adjuster is added to adjust the pH value to 7.5~8.5. The mixture is kept warm and stirred to obtain shellac ammonium salt base solution.

[0063] In this invention, the source of the dewaxed and bleached shellac is not particularly limited; it can be a commercially available product or prepared according to known methods in the art (such as shellac prepared by dewaxing, dechlorination, bleaching, etc.).

[0064] In this invention, the water is preferably deionized water.

[0065] In this invention, the pH adjuster is preferably an alkaline adjuster, more preferably ammonia. The concentration of the ammonia is preferably 8% to 25% (mass fraction), specifically 8%, 10%, 15%, 20%, 25%, more preferably 15%. Adding the pH adjuster to adjust the pH of the system to 7.5 to 8.5 ensures complete dissolution of the shellac and achieves optimal results. If the pH is too high, the polymerization rate will be too fast when adding the inorganic precursor hydrolysate, leading to excessive local cross-linking; if the pH is too low, the bleached shellac will not dissolve completely. Specifically, the pH can be 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, or 8.5, preferably 7.5 to 8.0. In this invention, the pH adjuster is preferably added dropwise.

[0066] In this invention, the heating temperature is preferably 60~80℃, specifically 60℃, 65℃, 70℃, 75℃, or 80℃. The stirring speed during heat preservation is preferably 300~600 rpm, specifically 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, or 600 rpm. The mixture is kept at this temperature and stirred until completely clear, yielding a shellac ammonium salt-based solution containing CMC-Na.

[0067] Regarding step S3 :

[0068] S3 (Pre-hydrolysis of inorganic precursor): Nano-silica sol and methyltrimethoxysilane are mixed, and an acidic catalyst is added to adjust the pH to 5.0~6.0. The mixture is stirred and pre-hydrolyzed to obtain a pre-hydrolyzed solution.

[0069] In this invention, the SiO2 particle size of the nano-silica sol is 5-40 nm, and the SiO2 content is 10%-40%. Specifically, the particle size can be 5 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, or 40 nm. The SiO2 content can be 10%, 15%, 20%, 25%, 30%, 35%, or 40%. There are no special restrictions on the source of the nano-silica sol; it can be a commercially available product.

[0070] In this invention, the source of the methyltrimethoxysilane (MTMS) is not particularly limited, and it can be a commercially available product.

[0071] In this invention, the acidic catalyst is preferably acetic acid and / or phosphoric acid. The concentration of the acetic acid is preferably 5% to 10% (w / w), specifically 5%, 6%, 7%, 8%, 9%, or 10%. The concentration of the phosphoric acid is preferably 1% to 5% (w / w), specifically 1%, 2%, 3%, 4%, or 5%. In this invention, the acidic catalyst is used in trace amounts to adjust the pH value to 5.0~6.0, specifically 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, and 6.0. Controlling the pH within this range allows MTMS to have a better hydrolysis rate. Under these pH conditions, the condensation reaction rate is not fast, and the silanol groups carried after hydrolysis can react more uniformly with the silanol groups of the acidic silica sol, while retaining some active groups to participate in subsequent reactions. If the pH value is too low, the MTMS hydrolysis rate will be too fast, resulting in uneven dispersion and excessive self-condensation instead of hydrophobic modification and crosslinking of the silica sol. If the pH value is too high, the condensation rate will be too fast, easily leading to excessive self-condensation and localized excessive crosslinking.

[0072] In this invention, the stirring speed for the pre-hydrolysis is preferably 500-1000 rpm, specifically 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm, or 1000 rpm. The pre-hydrolysis time is preferably 30-60 min, specifically 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min. In this invention, the pre-hydrolysis is carried out at room temperature, specifically 25-35°C, specifically 25°C, 30°C, or 35°C. After the above pre-hydrolysis, a pre-hydrolyzed solution is obtained.

[0073] Regarding step S4 :

[0074] S4 (Coupling Activation): The pre-hydrolyzed solution obtained in step S3 is mixed with a silane coupling agent to obtain an activated solution.

[0075] In this invention, the preferred silane coupling agent is KH-570 and / or KH-550. KH-570 is a methacryloyloxy silane carrying a methacryloyloxypropyl group, and KH-550 is an amino silane carrying a highly polar and active amino group. Both can chemically bond with the carboxyl and hydroxyl groups on the shellac molecular chain to achieve organic-inorganic interface bridging. If other coupling agents are used, such as KH-792 of the same class, although its chemical structure is similar to KH-550, its double amino structure is prone to premature reaction with the carboxyl groups in shellac, leading to a sharp increase in system viscosity or even gelation. Other types of silane coupling agents (such as epoxy-based and vinyl-based agents) are not suitable for the system environment of this invention.

[0076] In this invention, the mixing method is preferably stirring. The stirring speed is preferably 500-1000 rpm, specifically 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm, or 1000 rpm; the stirring time is preferably 10-20 minutes, specifically 10 minutes, 15 minutes, or 20 minutes. After mixing, an activated solution is obtained.

[0077] Regarding step S5 :

[0078] S5 (In-situ Hybridization Reaction): The shellac ammonium salt base solution obtained in step S2 is mixed with the activation solution obtained in step S4, and the mixture is reacted to obtain a hybrid solution.

[0079] In this invention, the preferred mixing method is to add the activation solution obtained in step S4 dropwise to the shellac ammonium salt base solution obtained in step S2.

[0080] In this invention, the mixing temperature is preferably 40~60℃, specifically 40℃, 45℃, 50℃, 55℃, or 60℃.

[0081] In this invention, the reaction temperature is preferably 40~60℃, specifically 40℃, 45℃, 50℃, 55℃, or 60℃. The reaction time is preferably 3~5h, specifically 3h, 3.5h, 4h, 4.5h, or 5h.

[0082] In this invention, step S5 preferably includes: adding the activation solution obtained in step S4 dropwise to the shellac ammonium salt base solution obtained in step S2 at 40~60℃, and keeping it at this temperature for 3~5 hours to obtain a hybrid solution.

[0083] Regarding step S6 :

[0084] S6 (Additive compounding and finished product): The hybrid liquid obtained in step S5 is mixed with additives to obtain a water-based shellac-nano-silicon composite coating.

[0085] In this invention, the additives preferably include a bactericide, a leveling agent, and a defoamer. The bactericide is preferably an isothiazolinone bactericide, and in some embodiments of this invention, it is Nipacide KBS from Clariant, Germany. The leveling agent is preferably a silicone-modified polyether, and in some embodiments of this invention, it is Evonik Tego Glide 450 from Germany. The defoamer is preferably a water-based silicone, and in some embodiments of this invention, it is Evonik Tego Airex 900 from Germany.

[0086] In this invention, the mixing temperature is preferably ≤40℃. If the temperature of the hybrid liquid obtained in step S5 is 40℃, the additive can be introduced directly; if its temperature is higher than 40℃, it should be cooled to below 40℃ first, and then the additive should be introduced. The temperature is more preferably 25~40℃, specifically 25℃, 30℃, 35℃, or 40℃.

[0087] In this invention, stirring is preferably performed during the mixing process. The stirring speed is preferably 200-500 rpm, specifically 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm. After uniform stirring, the material is filtered out. The filter screen used for filtration is preferably an 80-300 mesh screen, specifically 80 mesh, 100 mesh, 150 mesh, 200 mesh, 250 mesh, or 300 mesh, more preferably 200 mesh. After the above treatment, a water-based shellac-nano-silica composite coating is obtained.

[0088] In this invention, the amounts of materials used in each of the above steps are as follows:

[0089] Dewaxed and bleached shellac: 10-20 parts by weight;

[0090] CMC-Na: 0.3~1.5 parts by weight;

[0091] Water: 55-70 parts by weight;

[0092] Nano silica sol: 5~15 parts by weight;

[0093] Methyltrimethoxysilane: 2-8 parts by weight;

[0094] Silane coupling agent: 0.5~2 parts by weight;

[0095] Additives: 0.4~0.8 parts by weight.

[0096] The amount of the dewaxed bleached shellac used is 10-20 parts by weight, specifically 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 parts.

[0097] The amount of CMC-Na used is 0.3 to 1.5 parts by weight, specifically 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, and 1.5 parts.

[0098] The amount of water used is 55-70 parts by mass, meaning the total amount of water (i.e., the sum of the amounts of water used in step S1 and step S2) is 55-70 parts, specifically 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, or 70 parts. In step S1, the water accounts for 30%-70% (w / w) of the total water volume, specifically 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. Preferably, the concentration of the solution obtained in step S1 is 1.0%-2.5% (w / w), specifically 1.0%, 1.5%, 2.0%, or 2.5%, more preferably 2%. The remainder (i.e., 30%-70%) is the water in step S2.

[0099] The amount of the nano-silica sol used is 5 to 15 parts by weight, specifically 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 parts.

[0100] The amount of methyltrimethoxysilane used is 2 to 8 parts by weight, specifically 2, 3, 4, 5, 6, 7, or 8 parts.

[0101] The amount of the silane coupling agent is 0.5 to 2 parts by weight, specifically 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0 parts.

[0102] The additive is used in an amount of 0.4 to 0.8 parts by weight, specifically 0.4, 0.5, 0.6, 0.7, or 0.8 parts. The bactericide is used in an amount of 0.1 to 0.2 parts by weight, specifically 0.1 or 0.2 parts. The leveling agent is used in an amount of 0.2 to 0.4 parts by weight, specifically 0.2, 0.3, or 0.4 parts. The defoamer is used in an amount of 0.1 to 0.2 parts by weight, specifically 0.1, 0.15, or 0.2 parts.

[0103] In addition to the substances mentioned above, a pH adjuster is used in step S2, and an acidic catalyst is used in step S3. Both are mainly used to adjust the pH value, and their dosage is sufficient to achieve the target pH value. For example, the amount of the pH adjuster is approximately 1.0 to 2.0 parts, and the amount of the acidic catalyst is approximately 0.1 parts.

[0104] [Second aspect] The present invention also provides an aqueous shellac-nanosilicon composite coating, which is prepared by the preparation method described in the above technical solution.

[0105] [Third Aspect] The present invention also provides a packaging material, comprising a substrate and a coating laminated to the surface of the substrate; wherein the coating is formed by the water-based shellac-nanosilica composite coating described in the above-mentioned technical solution. In the present invention, the packaging material is preferably a food packaging material. The substrate is preferably paper.

[0106] The core mechanism of the water-based shellac-nanosilica composite coating provided by this invention lies in the synergistic effect of constructing an organic-inorganic hybrid interpenetrating network and introducing pseudoplastic rheological regulation. First, MTMS is pre-hydrolyzed under acidic conditions to generate silanol groups. On one hand, these silanol groups condense with the silanol groups on the surface of the nanosilica sol, forming a rigid inorganic Si-O-Si network framework, endowing the coating with high hardness and density. On the other hand, the methyl groups in the MTMS molecules introduce hydrophobic groups, reducing the surface energy of the coating and achieving excellent water resistance. Simultaneously, the amino or methacryloyloxy groups in the silane coupling agent (KH-550 / KH-570) react with the carboxyl and hydroxyl groups on the shellac molecular chain, and the silanol groups at the other end condense with the inorganic network, achieving chemical bonding between the organic shellac phase and the inorganic silicon network. This solves the problems of poor interfacial compatibility and easy phase separation caused by physical blending, ultimately forming an interpenetrating network structure with shellac as the continuous phase, nanosilica sol as the dispersed phase, and MTMS as the crosslinking points. Meanwhile, CMC-Na was introduced as a rheology modifier to construct a pseudoplastic fluid structure to resolve the conflict between storage and construction. After CMC-Na dissolves in water, its long molecular chains interact with water molecules, shellac ammonium salt, and silica sol particles through hydrogen bonds to form a three-dimensional network structure. This locks the nanoparticles within the system in a static state, preventing them from settling or agglomerating due to gravity, thus achieving long-term storage stability. In addition, the water-retention properties of CMC-Na delay water evaporation, providing a longer reaction time for the full condensation of MTMS and reducing microcracks. At the same time, its molecular chains interweave within the organic-inorganic network, further filling microscopic voids through hydrogen bonds, thereby improving the density and barrier properties of the coating. In summary, MTMS and silica sol form a hydrophobic rigid framework, CMC-Na provides rheological regulation and network enhancement, silane coupling agents provide interfacial bridges, and shellac provides a bio-based film-forming matrix. The synergistic effect of these four components achieves a comprehensive performance breakthrough of "no sedimentation during storage and water and oil resistance in the coating film," solving the long-standing technical pain points of existing waterborne shellac coatings, such as poor hydrophobicity and high-temperature water resistance.

[0107] Compared with the prior art, the present invention has the following beneficial effects:

[0108] (1) Excellent hydrophobicity and high temperature water resistance: Through the synergistic effect of MTMS and silica sol, when the coating of the present invention is applied to the surface of food packaging base paper, a dense organic-inorganic hybrid network is formed in the shellac matrix coating, which significantly improves the hydrophobicity and boiling water resistance of the coating film.

[0109] (2) Excellent storage stability: The three-dimensional network structure formed by CMC-Na effectively locks in the nano-silica sol and MTMS hydrolysis products, preventing them from settling and agglomerating. After 30 days of heat storage at 50℃, the emulsion showed no sedimentation or stratification.

[0110] The test results show that the coating of the present invention does not show any sedimentation or stratification after 30 days of heat storage at 50℃, the Kit value reaches 8 or above, the contact angle is above 90°, and the boiling water resistance time reaches 30 minutes or above, demonstrating excellent storage stability, oil resistance and high temperature water resistance.

[0111] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0112] Example 1

[0113] 1. Raw materials:

[0114] Dewaxed and bleached shellac: 10 parts;

[0115] CMC-Na (HV type): 0.3 parts;

[0116] Deionized water: 60 parts (30% in step S1, 70% in step S2);

[0117] Nano silica sol (particle size 15nm, SiO2 content 20%): 5 parts;

[0118] MTMS: 2 copies;

[0119] Silane coupling agent KH-570: 0.5 parts;

[0120] Nipacide KBS bactericide: 0.2 parts;

[0121] Leveling agent Tego Glide 450: 0.3 parts;

[0122] Defoamer Tego Airex 900: 0.1 parts.

[0123] In addition, a pH adjuster and an acidic catalyst were used to adjust the pH value to the target value. In this embodiment, the pH adjuster was ammonia water (15%), used to adjust the pH value to 8.0, with an amount of approximately 1.0 part. The acidic catalyst was acetic acid, used to adjust the pH value to 5.0.

[0124] 2. Preparation of water-based shellac-nano-silicon composite coating:

[0125] S1 (CMC-Na pre-dissolved): Take 30% of the total water volume of deionized water, slowly add CMC-Na to it, heat to 60℃, and stir at 1200rpm until completely dissolved to obtain a translucent liquid.

[0126] S2 (Preparation of shellac ammonium salt solution): Mix dewaxed bleached shellac, the remaining deionized water and the shellac solution obtained in step S1, heat to 70°C, add ammonia water dropwise to adjust the pH value to 8.0, keep warm and stir (300 rpm) until completely clear to obtain shellac ammonium salt base solution.

[0127] S3 (Pre-hydrolysis of inorganic precursor): Mix nano-silica sol and MTMS, add acetic acid to adjust the pH to 5.0, stir at room temperature (25℃) (600 rpm) for 45 min to obtain pre-hydrolyzed solution.

[0128] S4 (Coupling Activation): Add silane coupling agent KH-570 to the pre-hydrolyzed solution obtained in step S3, and stir at 600 rpm for 15 min to obtain the activated solution.

[0129] S5 (in-situ hybridization reaction): At 45°C, the activation solution obtained in step S4 is added dropwise to the shellac ammonium salt base solution obtained in step S2, and the reaction is maintained at this temperature for 4 hours to obtain the hybrid solution.

[0130] S6 (Additive compounding and finished product): Cool to 40℃, add bactericide, leveling agent and defoamer in sequence, stir at low speed (250rpm) for 20min, and pass through a 200-mesh filter to obtain water-based shellac-nano-silicon composite coating.

[0131] Example 2

[0132] 1. Raw materials:

[0133] Dewaxed and bleached shellac: 12 parts;

[0134] CMC-Na (HV type): 0.6 parts;

[0135] Deionized water: 65 parts (30% in step S1, 70% in step S2);

[0136] Nano silica sol (particle size 15nm, SiO2 content 20%): 8 parts;

[0137] MTMS: 4 copies;

[0138] Silane coupling agent KH-550: 1.0 part;

[0139] Nipacide KBS, a fungicide: 0.3 parts;

[0140] Leveling agent Tego Glide 450: 0.5 parts;

[0141] Defoamer Tego Airex 900: 0.2 parts.

[0142] In addition, a pH adjuster and an acidic catalyst were used to adjust the pH value to the target value. In this embodiment, the pH adjuster was ammonia water (15%), used to adjust the pH value to 8.0, with an amount of approximately 1.2 parts. The acidic catalyst was acetic acid, used to adjust the pH value to 5.5.

[0143] 2. Preparation of water-based shellac-nano-silicon composite coating:

[0144] S1 (CMC-Na pre-dissolved): Take 30% of the total water volume of deionized water, slowly add CMC-Na to it, heat to 60℃, and stir at 1000rpm until completely dissolved to obtain a translucent gel.

[0145] S2 (Preparation of shellac ammonium salt solution): Mix dewaxed bleached shellac, the remaining deionized water and the shellac solution obtained in step S1, heat to 60°C, add ammonia water dropwise to adjust the pH value to 8.0, keep warm and stir (400 rpm) until completely clear to obtain shellac ammonium salt base solution.

[0146] S3 (Pre-hydrolysis of inorganic precursor): Mix nano-silica sol and MTMS, add acetic acid to adjust the pH to 5.5, stir at room temperature (25℃) (750 rpm) for 45 min to pre-hydrolyze and obtain the pre-hydrolysate.

[0147] S4 (Coupling Activation): Add silane coupling agent KH-550 to the pre-hydrolyzed solution obtained in step S3, and stir at 750 rpm for 20 min to obtain the activated solution.

[0148] S5 (in-situ hybridization reaction): At 40°C, the activation solution obtained in step S4 is added dropwise to the shellac ammonium salt base solution obtained in step S2, and the reaction is maintained at this temperature for 5 hours to obtain the hybrid solution.

[0149] S6 (Additive compounding and finished product): Cool to 35℃, add bactericide, leveling agent and defoamer in sequence, stir at low speed (200rpm) for 20min, and pass through a 200-mesh filter to obtain water-based shellac-nano-silicon composite coating.

[0150] Example 3

[0151] 1. Raw materials:

[0152] Dewaxed and bleached shellac: 15 parts;

[0153] CMC-Na (HV type): 0.9 parts;

[0154] Deionized water: 65 parts (30% in step S1, 70% in step S2);

[0155] Nano silica sol (particle size 15nm, SiO2 content 20%): 10 parts;

[0156] MTMS: 5 copies;

[0157] Silane coupling agent KH-570: 1.5 parts;

[0158] Nipacide KBS, a fungicide: 0.3 parts;

[0159] Leveling agent Tego Glide 450: 0.6 parts;

[0160] Defoamer Tego Airex 900: 0.2 parts.

[0161] In addition, a pH adjuster and an acidic catalyst were used to adjust the pH value to the target value. In this embodiment, the pH adjuster was ammonia water (15%), used to adjust the pH value to 8.0, with an amount of approximately 1.5 parts. The acidic catalyst was acetic acid, used to adjust the pH value to 5.5.

[0162] 2. Preparation of water-based shellac-nano-silicon composite coating:

[0163] S1 (CMC-Na pre-dissolved): Take 30% of the total water volume of deionized water, slowly add CMC-Na to it, heat to 60℃, and stir at 1500rpm until completely dissolved to obtain a translucent gel.

[0164] S2 (Preparation of shellac ammonium salt solution): Mix dewaxed bleached shellac, the remaining deionized water and the shellac solution obtained in step S1, heat to 80°C, add ammonia water dropwise to adjust the pH value to 8.0, keep warm and stir (500 rpm) until completely clear to obtain shellac ammonium salt base solution.

[0165] S3 (Pre-hydrolysis of inorganic precursor): Mix nano-silica sol and MTMS, add acetic acid to adjust the pH to 5.5, stir at room temperature (25℃) (800 rpm) for 50 min to pre-hydrolyze and obtain the pre-hydrolysate.

[0166] S4 (Coupling Activation): Add silane coupling agent KH-570 to the pre-hydrolyzed solution obtained in step S3, and stir at 500 rpm for 10 min to obtain the activated solution.

[0167] S5 (in-situ hybridization reaction): At 60°C, the activation solution obtained in step S4 is added dropwise to the shellac ammonium salt base solution obtained in step S2, and the reaction is maintained at this temperature for 3 hours to obtain the hybrid solution.

[0168] S6 (Auxiliary agent compounding and finished product): Cool to 35℃, add bactericide, leveling agent and defoamer in sequence, stir at low speed (300rpm) for 20min, and pass through a 200-mesh filter to obtain water-based shellac-nano-silicon composite coating.

[0169] Example 4

[0170] 1. Raw materials:

[0171] Dewaxed and bleached shellac: 20 parts;

[0172] CMC-Na (HV type): 1.5 parts;

[0173] Deionized water: 70 parts (30% in step S1 and 70% in step S2);

[0174] Nano silica sol (particle size 15nm, SiO2 content 20%): 15 parts;

[0175] MTMS: 8 copies;

[0176] Silane coupling agent KH-550: 2.0 parts;

[0177] Nipacide KBS bactericide: 0.5 parts;

[0178] Leveling agent Tego Glide 450: 1.0 part;

[0179] Defoamer Tego Airex 900: 0.3 parts.

[0180] In addition, a pH adjuster and an acidic catalyst were used to adjust the pH value to the target value. In this embodiment, the pH adjuster was ammonia water (15%), used to adjust the pH value to 8.0, with an amount of approximately 2.0 parts. The acidic catalyst was acetic acid, used to adjust the pH value to 6.0.

[0181] 2. Preparation of water-based shellac-nano-silicon composite coating:

[0182] S1 (CMC-Na pre-dissolved): Take 30% of the total water volume of deionized water, slowly add CMC-Na to it, heat to 60℃, and stir at 1200rpm until completely dissolved to obtain a translucent liquid.

[0183] S2 (Preparation of shellac ammonium salt solution): Mix dewaxed bleached shellac, the remaining deionized water and the shellac solution obtained in step S1, heat to 70°C, add ammonia water dropwise to adjust the pH value to 8.0, keep warm and stir (600 rpm) until completely clear to obtain shellac ammonium salt base solution.

[0184] S3 (Pre-hydrolysis of inorganic precursor): Mix nano-silica sol and MTMS, add acetic acid to adjust the pH to 6.0, stir at room temperature (25℃) (800 rpm) for 45 min to obtain pre-hydrolyzed solution.

[0185] S4 (Coupling Activation): Add silane coupling agent KH-550 to the pre-hydrolyzed solution obtained in step S3, and stir at 800 rpm for 15 min to obtain the activated solution.

[0186] S5 (in-situ hybridization reaction): At 40°C, the activation solution obtained in step S4 is added dropwise to the shellac ammonium salt base solution obtained in step S2, and the reaction is maintained at this temperature for 4 hours to obtain the hybrid solution.

[0187] S6 (Additive compounding and finished product): Cool to 35℃, add bactericide, leveling agent and defoamer in sequence, stir at low speed (500rpm) for 20min, and pass through a 200-mesh filter to obtain water-based shellac-nano-silicon composite coating.

[0188] Comparative Example 1

[0189] The method was implemented according to Example 3, except that CMC-Na was not introduced; specifically, step S1 was not performed during the preparation process, and step S2 was performed directly (without adding glue during the process) to dissolve the dewaxed bleached shellac in deionized water with ammonia.

[0190] Comparative Example 2

[0191] The method was implemented according to Example 3, except that MTMS was not introduced; specifically, MTMS was not added in step S3 of the preparation process.

[0192] Comparative Example 3

[0193] The method was implemented according to Example 3, except that: no nano-silica sol was introduced; specifically, no nano-silica sol was added in step S3 of the preparation process.

[0194] Comparative Example 4

[0195] The implementation follows Example 3, except that the silane coupling agent KH-570 in step S4 is replaced with silane coupling agent KH-792.

[0196] Comparative Example 5

[0197] The procedure was carried out according to Example 3, except that the methyltrimethoxysilane in step S3 was replaced with another organosilane (ethyl orthosilicate).

[0198] Performance testing :

[0199] The coating samples obtained from each embodiment and comparative example were subjected to performance tests according to the following method. Preparation of the coated paper for testing: 80 g / m²... 2 Using white kraft paper as the substrate, two coats of coating are applied to one of the surfaces, with a total dry coating weight of 10 g / m². 2 After drying at 105℃ for 30 seconds, three parallel samples were tested in each group, and the average value was taken.

[0200] (1) Storage stability: In accordance with GB / T 6753.3-1906 standard, the coating was sealed in a transparent glass bottle and stored in a constant temperature oven at 50℃ for 30 days. The sedimentation, stratification and mold growth were observed.

[0201] (2) Grease barrier properties: According to the TAPPI T559 cm-02 standard (Kit method), different numbered test liquids were dropped onto the surface of the coated paper sample, and the wetting situation was observed after 15 seconds. The highest test liquid number that did not wet the coating was indicated (the higher the value, the better the grease resistance).

[0202] (3) Contact angle: Using a contact angle measuring instrument (Dongguan Shengding Precision Instruments Co., Ltd., model SDC-350), 2μL of distilled water was added to the surface of the coated paper at room temperature, and the measurement was taken after standing for 10s. The average value of 5 measurements was taken.

[0203] (4) Boiling water resistance: According to GB / T 27590-2022 "Paper Cup", the coated paper is folded into a square box with a height of 5cm, water at 95±5℃ is poured in, and the time when the coating surface at the bottom of the box begins to turn white or leak (maximum time, 30min).

[0204] The test results for the above tests are shown in Table 1.

[0205] Table 1: Performance Test Results

[0206]

[0207] The test results above show that Examples 1-4 of this invention exhibited no sedimentation or stratification after 30 days of heat storage at 50℃, with Kit values ​​exceeding 8, contact angles exceeding 90°, and no whitening or leakage after 30 minutes of boiling water resistance, demonstrating excellent storage stability, oil resistance, hydrophobicity, and high-temperature water resistance. Comparative Examples 1 (without CMC-Na) and 2 (without MTMS) showed significant sedimentation. The oil barrier properties of Comparative Example 1 (without CMC-Na), the hydrophobicity and high-temperature water resistance of Comparative Example 2 (without MTMS) decreased significantly, and the hydrophobicity and high-temperature water resistance of Comparative Example 3 (without silica sol) also decreased. The results indicate that CMC-Na, silica sol, and MTMS synergistically impart excellent storage stability, oil resistance, and high-temperature water resistance to the coating. The significantly reduced storage stability of Comparative Examples 4-5 proves that the use of specific silane coupling agents and organosilanes in this invention is beneficial for ensuring the storage stability of the coating.

[0208] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing an aqueous shellac-nanosilica composite coating, characterized in that, Includes the following steps: S1. Mix sodium carboxymethyl cellulose with water, heat to dissolve, and form a gel. S2. Mix the dewaxed bleached shellac, water and the resin solution obtained in step S1, heat, add pH adjuster to adjust the pH value to 7.5~8.5, keep warm and stir to obtain shellac ammonium salt base solution. S3. Mix nano-silica sol and methyltrimethoxysilane, add an acidic catalyst to adjust the pH to 5.0~6.0, stir and pre-hydrolyze to obtain a pre-hydrolyzed solution; S4. Mix the pre-hydrolyzed solution obtained in step S3 with the silane coupling agent to obtain the activation solution; S5. Mix the shellac ammonium salt base solution obtained in step S2 with the activation solution obtained in step S4, and react to obtain a hybrid solution; S6. Mix the hybrid liquid obtained in step S5 with the additive to obtain an aqueous shellac-nanosilicon composite coating.

2. The preparation method according to claim 1, characterized in that, The quantities of materials used in each step are as follows: Dewaxed and bleached shellac: 10-20 parts by weight; Sodium carboxymethyl cellulose: 0.3~1.5 parts by weight; Water: 55-70 parts by weight; Nano silica sol: 5~15 parts by weight; Methyltrimethoxysilane: 2-8 parts by weight; Silane coupling agent: 0.5~2 parts by weight; Additives: 0.4~0.8 parts by weight.

3. The preparation method according to claim 1, characterized in that, In step S4, the silane coupling agent is KH-570 and / or KH-550.

4. The preparation method according to claim 1, characterized in that, In step S1, the heating and melting temperature is 50~80℃.

5. The preparation method according to claim 1, characterized in that, In step S2: The pH adjuster is ammonia water; The heating temperature is 60~80℃.

6. The preparation method according to claim 1, characterized in that, In step S3: The SiO2 particles in the nano-silica sol have a particle size of 5-40 nm and a SiO2 content of 10%-40%. The acidic catalyst is acetic acid and / or phosphoric acid; The stirring speed for the pre-hydrolysis is 500~1000 rpm, and the time is 30~60 min.

7. The preparation method according to claim 1, characterized in that, In step S5: The mixing temperature is 40~60℃; The reaction is carried out at a temperature of 40-60°C for 3-5 hours.

8. The preparation method according to claim 1, characterized in that, In step S6: The additives include bactericides, leveling agents, and defoamers; The mixing temperature is ≤40℃.

9. A water-based shellac-nanosilicon composite coating, characterized in that, It is prepared by any one of claims 1 to 8.

10. A packaging material, characterized in that, It includes a substrate and a coating compounded on the surface of the substrate; wherein the coating is formed by the water-based shellac-nanosilicon composite coating of claim 9.

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