A coating for paper substrates surfaces and paper products for food packaging comprising it

Abstract

The present application belongs to the technical field of paper-based packaging materials, and particularly relates to a coating layer for the surface of a paper base material and a paper product for food packaging comprising the same. The present application forms a biodegradable coating wax composition by using a fatty alcohol, a natural plant resin, a heat-resistant modifier and an antioxidant, and controls the heating and melting mixing and hot melt coating process, so that a wax coating layer is formed on the surface of the paper base material. The coating layer can reduce the influence of water evaporation, additive residue and drying film formation on layer continuity in the emulsion coating system, and has the properties of waterproofness, oil resistance, heat-resistant oil and antioxidant property, and is suitable for paper products for food packaging such as hamburger paper and hot dog paper.

Description

Technical Field

[0001] This invention belongs to the technical field of paper-based packaging materials, specifically relating to a coating layer for the surface of a paper substrate and paper products for food packaging including the coating layer. Background Technology

[0002] Paper-based packaging materials are widely available, easy to process, recyclable, and readily accepted by consumers, and are therefore widely used in food packaging, takeaway packaging, baking packaging, and other single-use packaging applications. However, paper substrates are formed from interwoven fibers, resulting in numerous pores on the surface and inside. When in direct contact with water-, oil-, or temperature-sensitive foods, they are prone to water and oil absorption, seepage, softening, and reduced packaging strength. Therefore, forming a coating layer on the paper substrate surface that provides waterproof, oil-proof, and heat-resistant oil properties is an important way to improve the performance of paper packaging.

[0003] Traditional paper-based packaging often uses plastic lamination, petroleum-based wax coatings, or other synthetic barrier layers to impart functionality to paper. However, these materials still have limitations in terms of biodegradability, recyclability, and food contact safety. With the increasing demand for green packaging and reducing the use of petroleum-based materials, biodegradable wax materials, due to their combination of wax barrier properties and environmental friendliness, are gradually becoming an important development direction for functional coating materials in paper-based packaging.

[0004] Currently, various treatment methods have been proposed for the application of wax materials on paper substrates. For example, traditional wax materials such as paraffin wax and microcrystalline wax can be used to treat paper substrates for moisture or oil resistance, while plant-derived waxes, bio-based waxes, or other biodegradable wax materials can replace some petroleum-based materials. To facilitate coating processing, existing technologies often employ emulsion-type or water-based routes. This involves converting hydrophobic wax materials into water-based emulsions or dispersion systems through emulsification and dispersion, then applying them to the paper substrate surface, and drying them to form a coating layer with a certain barrier effect. The technical focus of this type of route is usually on improving the dispersion stability of wax materials in the aqueous phase, improving the storage state of the emulsion, and meeting the requirements of water-based coating processes. However, the essence of emulsion-type or water-based routes is to first disperse the hydrophobic wax material in the aqueous phase, and then re-form a coating on the paper substrate surface through coating and drying processes. For paper substrates used in food packaging, while this approach enables the application of wax materials, the formation of the coating depends not only on the wax material itself but also on factors such as the emulsion system, paper substrate absorption, moisture evaporation, drying and film formation, and additive residues. For paper products used in food packaging that require waterproofing, oil resistance, and heat resistance, improvements focused solely on emulsion stability or the ease of water-based coating are insufficient to fully leverage the lamination effect of wax materials as hydrophobic barrier materials, nor can they guarantee the formation of a stable and effective coating on the paper substrate surface.

[0005] Therefore, it is necessary to provide a coating layer for the surface of a paper substrate that can be formed on the surface of the paper substrate by hot melt coating, and to give the paper products for food packaging that include the coating layer waterproof, oil-proof and heat-resistant oil properties. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a coating layer for the surface of paper substrates and paper products for food packaging comprising the same. By defining the composition of the coating wax composition and the boundaries of the high-temperature zone, this invention enables the formation of a stable and effective wax coating layer on the surface of the paper substrate, providing an innovative solution for achieving excellent waterproof, oil-proof, and heat-resistant oil properties.

[0007] The first objective of this invention is achieved through the following technical solution:

[0008] A coating layer for a paper substrate surface, the coating layer being formed by hot-melt application of a biodegradable coating wax composition onto the paper substrate surface, the biodegradable coating wax composition comprising the following components in parts by weight:

[0009] Fatty alcohols: 50-90 parts;

[0010] Natural plant resin: 5-25 parts;

[0011] Heat-resistant modifier: 5-25 parts;

[0012] Antioxidant: 0.05-0.2 parts;

[0013] The fatty alcohol is selected from one or more of stearyl alcohol, arachidyl alcohol, and behenyl alcohol;

[0014] The coating layer is formed by heating and melting fatty alcohol, natural plant resin, heat-resistant modifier and antioxidant at 80-110°C to obtain the biodegradable coating wax composition, and then maintaining the biodegradable coating wax composition at 100-110°C and hot-melting it onto the surface of a paper substrate to form the coating layer.

[0015] The cumulative heating time of the biodegradable coating wax composition during the heating, melting, mixing, and hot-melt coating process is 15-20 hours.

[0016] In this invention, the heating and melting mixing time refers to the duration of melting and mixing of each component after the temperature of each component reaches the specified heating and melting mixing temperature; the hot-melt coating time refers to the duration from the start of applying the molten coating wax composition to the surface of the paper substrate to the completion of the batch coating. The sum of the heating and melting mixing time and the hot-melt coating time is the total time for heating and melting mixing and hot-melt coating.

[0017] In this paper, the time for a single hot-melt coating of the biodegradable coating wax composition onto the paper substrate surface is <1 hour after melting; the maximum overall heat preservation storage time for the same batch of molten biodegradable coating wax compositions is ≤5 hours.

[0018] Preferably, the coating amount of the biodegradable coating wax composition is 5-7 g / m² per unit area of ​​the paper substrate. 2 .

[0019] Preferably, the natural plant resin is selected from one or more of rosin resin, terpene resin, dammar resin, and copal resin.

[0020] More preferably, the natural plant resin is rosin resin.

[0021] Preferably, the heat-resistant modifier is selected from one or both of carnauba wax and hydrogenated castor oil.

[0022] More preferably, the heat-resistant modifier is carnauba wax.

[0023] Preferably, the antioxidant is selected from one or both of RIANOX 1010 and RIANOX 1076.

[0024] Preferably, the biodegradable coating wax composition comprises the following components in parts by weight: 65-90 parts of the fatty alcohol, 5-15 parts of the natural plant resin, 5-15 parts of the heat-resistant modifier, and 0.08-0.15 parts of the antioxidant.

[0025] Preferably, the water contact angle of the coating is >98° and the oil contact angle is >85°.

[0026] More preferably, the water contact angle of the coating layer is >100° and the oil contact angle is >90°.

[0027] Preferably, the dropping point of the biodegradable coating wax composition is >72°C.

[0028] Preferably, the biodegradable coating wax composition has a dynamic viscosity of 10.5-15.0 mPa·s at 100°C.

[0029] This method employs fatty alcohols, natural plant resins, heat-resistant modifiers, and antioxidants to form a biodegradable coating wax composition, which is then applied to the surface of a paper substrate via hot-melt coating. The fatty alcohols provide a long-chain hydrophobic structure, the natural plant resins regulate the viscosity, wetting and adhesion, and film continuity of the melt system, the heat-resistant modifiers improve the stability of the coating layer under hot oil conditions, and the antioxidants reduce the oxidation risk during the hot-melt process. Under the component and temperature conditions defined in this invention, the cumulative heating time simultaneously affects the compatibility and dispersion of each component, as well as the thermal oxidation state of the composition. When the cumulative heating time is less than 15 hours, the natural plant resins and antioxidants may not have achieved sufficient and uniform dispersion in the melt system formed by the fatty alcohols and heat-resistant modifiers. This can easily lead to uneven local component distribution and viscosity fluctuations in the melt, which is detrimental to uniform wetting and continuous coverage of the paper fiber surface during hot-melt coating and increases the risk of local defects in the coating layer. When the cumulative heating time exceeds 20 hours, the composition remains in the high-temperature molten state for too long, the protective effect of the antioxidant gradually weakens, the risk of thermal oxidation of fatty alcohols and natural plant resins increases, the melt is prone to darkening in color, odor change and decreased fluidity, which in turn affects the stability of hot melt coating and the waterproof and oil-proof performance of the resulting coating layer.

[0030] The second objective of this invention is achieved through the following technical solution:

[0031] A paper product for food packaging includes a paper substrate and the aforementioned coating layer, wherein the coating layer is disposed on at least one surface of the paper substrate.

[0032] Preferably, the paper substrate is hamburger paper, hot dog paper, sandwich wrapping paper, baking wrapping paper, or catering takeaway wrapping paper.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The coating layer of the present invention is formed by hot-melt coating of a biodegradable coating wax composition onto the surface of a paper substrate, which can avoid the influence of water evaporation, emulsifying agent residue and drying film formation process on the continuity of the coating layer in emulsion coating systems.

[0035] 2. The present invention enables the coating layer to form a wax barrier structure on the surface of a paper substrate by limiting the composition of the biodegradable coating wax composition, the heating and melting mixing temperature, the hot melt coating temperature and the total time.

[0036] 3. The preferred coating amount of the present invention is such that the coating layer can cover the surface of the paper substrate and reduce the impact of excessive coating amount on the cooling and shaping and flexibility of paper products.

[0037] 4. The coating of the present invention has surface properties of water contact angle > 98° and oil contact angle > 85°, and is suitable for paper products for food packaging that require waterproof and oil-proof properties.

[0038] 5. The food packaging paper products of the present invention can be used for hamburger paper, hot dog paper, sandwich wrapping paper, baking wrapping paper or catering takeaway wrapping paper. Attached Figure Description

[0039] Figure 1 This is a structural schematic diagram of the paper product for food packaging provided in this application, wherein 1 is the coating layer and 2 is the paper substrate;

[0040] Figure 2 The water contact angle test diagram of the paper product for food packaging prepared in Example 2;

[0041] Figure 3 The image shows the oil contact angle test result of the paper product for food packaging prepared in Example 2. Detailed Implementation

[0042] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with the embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0043] The materials used in the embodiments and comparative examples of this invention are described below:

[0044] Stearyl alcohol: purity ≥96%, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0045] Peanutyl alcohol: 98% purity, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0046] Behenol: 98% purity, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0047] Cetyl alcohol: purity ≥99%, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0048] Tetracosyl alcohol: 98% purity, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0049] Rosin resin: softening point 80-90℃, acid value ≤9.0 mgKOH / g, purchased from Guangxi Wuzhou Richeng Forest Products Chemical Co., Ltd.

[0050] Carnauba wax: melting point 80-86℃, acid value 0.2-0.7 mgKOH / g, purchased from FONCEPI, Brazil;

[0051] Hamburger paper for food packaging: basis weight 23g / m³2 Purchased from Zhejiang Hengda New Materials Co., Ltd.

[0052] It should be noted that the hot melt coating time in the embodiments and comparative examples of the present invention is less than 1 min, and the coating process of each group of samples is the same. Therefore, the hot melt coating time will not be listed separately in the following embodiments and comparative examples.

[0053] Example 1

[0054] The preparation method of the paper product for food packaging in Example 1 includes the following steps:

[0055] (1) Weigh 50 parts by weight of stearyl alcohol, 24.9 parts by weight of rosin resin, 25 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0056] (2) Mix the stearyl alcohol, rosin resin, carnauba wax and antioxidant weighed in step (1), heat to 105°C, and melt and stir at 105°C for 15 hours to fully melt and mix the components evenly to obtain the coating liquid.

[0057] (3) The coating solution obtained in step (2) is kept at 105°C and hot-melt coated onto the surface of hamburger paper for food packaging, with a coating amount of 6 g / m². 2 .

[0058] (4) After coating, the paper is cooled to room temperature so that the coating liquid forms a coating layer on the surface of the hamburger paper for food packaging, thus obtaining the paper product for food packaging of Example 1.

[0059] Example 2

[0060] The difference between the paper product for food packaging in Example 2 and that in Example 1 is the different component ratios; the other steps are the same as in Example 1.

[0061] (1) Weigh 70 parts by weight of stearyl alcohol, 14.9 parts by weight of rosin resin, 15 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0062] (2-4) Following the steps (2-4) of Example 1, the paper product for food packaging of Example 2 is obtained.

[0063] Example 3

[0064] The difference between the paper product for food packaging in Example 3 and that in Example 1 is the different component ratios; the other steps are the same as in Example 1.

[0065] (1) Weigh 89.9 parts by weight of stearyl alcohol, 5 parts by weight of rosin resin, 5 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0066] (2-4) Following the steps (2-4) of Example 1, the paper product for food packaging of Example 3 is obtained.

[0067] Example 4

[0068] The difference between the food packaging paper product in Example 4 and that in Example 2 is the type of fatty alcohol; the other steps are the same as in Example 2.

[0069] (1) Weigh 70 parts by weight of behenol, 14.9 parts by weight of rosin resin, 15 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0070] (2-4) Following the steps (2-4) of Example 1, the paper product for food packaging of Example 4 is obtained.

[0071] Example 5

[0072] The difference between the paper product for food packaging in Example 5 and that in Example 2 is the type of fatty alcohol; the other steps are the same as in Example 2.

[0073] (1) Weigh 70 parts by weight of peanut alcohol, 14.9 parts by weight of rosin resin, 15 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0074] (2-4) Following the steps (2-4) of Example 1, the paper product for food packaging of Example 5 is obtained.

[0075] Comparative Example 1

[0076] The difference between the food packaging paper product of Comparative Example 1 and that of Example 2 lies in the type of fatty alcohol; the other steps are the same as in Example 2.

[0077] (1) Weigh 70 parts by weight of cetyl alcohol, 14.9 parts by weight of rosin resin, 15 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0078] (2-4) Following the steps (2-4) of Example 1, the paper product for food packaging of Comparative Example 1 was obtained.

[0079] Comparative Example 2

[0080] The difference between the food packaging paper products of Comparative Example 2 and those of Example 2 lies in the type of fatty alcohol; the other steps are the same as in Example 2.

[0081] (1) Weigh 70 parts by weight of tetracosyl alcohol, 14.9 parts by weight of rosin resin, 15 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0082] (2-4) Following the steps (2-4) of Example 1, the paper products for food packaging of Comparative Example 2 were obtained.

[0083] Comparative Example 3

[0084] The difference between the food packaging paper product of Comparative Example 3 and Example 1 lies in the different component ratios; the other steps are the same as in Example 1.

[0085] (1) Weigh 45 parts by weight of stearyl alcohol, 27.4 parts by weight of rosin resin, 27.5 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0086] (2-4) Following the steps (2-4) of Example 1, the paper product for food packaging of Comparative Example 3 was obtained.

[0087] Comparative Example 4

[0088] The difference between the food packaging paper product of Comparative Example 4 and Example 3 lies in the different component ratios; the other steps are the same as in Example 3.

[0089] (1) Weigh 95 parts by weight of stearyl alcohol, 2.4 parts by weight of rosin resin, 2.5 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0090] (2-4) Following the steps (2-4) of Example 1, the paper products for food packaging of Comparative Example 4 were obtained.

[0091] Comparative Example 5

[0092] The difference between the food packaging paper product of Comparative Example 5 and Example 2 lies in the different component ratios; the other steps are the same as in Example 2.

[0093] (1) Weigh 70 parts by weight of stearyl alcohol, 26.9 parts by weight of rosin resin, 3 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0094] (2-4) Following the steps (2-4) of Example 1, the paper products for food packaging of Comparative Example 5 were obtained.

[0095] Comparative Example 6

[0096] The difference between the food packaging paper product of Comparative Example 6 and Example 2 lies in the different component ratios; the other steps are the same as in Example 2.

[0097] (1) Weigh 70 parts by weight of stearyl alcohol, 3 parts by weight of rosin resin, 26.9 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0098] (2-4) Following the steps (2-4) of Example 1, the paper product for food packaging of Comparative Example 6 was obtained.

[0099] Comparative Example 7

[0100] The difference between the food packaging paper product of Comparative Example 7 and Example 2 lies in the different melt mixing temperature in step (2) and the different hot melt coating temperature in step (3). The other steps are the same as those of Example 2.

[0101] (1) Weigh 70 parts by weight of stearyl alcohol, 14.9 parts by weight of rosin resin, 15 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0102] (2) Mix the stearyl alcohol, rosin resin, carnauba wax and antioxidant weighed in step (1), heat to 130°C, and melt and stir at 130°C for 15 hours to fully melt and mix the components to obtain the coating liquid.

[0103] (3) The coating solution obtained in step (2) is kept at 130°C and hot-melt coated onto the surface of hamburger paper for food packaging, with a coating amount of 6 g / m². 2 .

[0104] (4) After coating, the paper is cooled to room temperature so that the coating liquid forms a coating layer on the surface of the hamburger paper for food packaging, thus obtaining the paper product for food packaging of Comparative Example 7.

[0105] Comparative Example 8

[0106] The difference between the food packaging paper product of Comparative Example 8 and Example 2 is the different melt mixing time in step (2), while the other steps are the same as in Example 2:

[0107] (1) Weigh 70 parts by weight of stearyl alcohol, 14.9 parts by weight of rosin resin, 15 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0108] (2) Mix the stearyl alcohol, rosin resin, carnauba wax and antioxidant weighed in step (1), heat to 105°C, and melt and stir at 105°C for 30 hours to obtain the coating liquid.

[0109] (3) The coating solution obtained in step (2) is kept at 105°C and hot-melt coated onto the surface of hamburger paper for food packaging, with a coating amount of 6 g / m². 2 .

[0110] (4) After coating, the paper is cooled to room temperature so that the coating liquid forms a coating layer on the surface of the hamburger paper for food packaging, thus obtaining the paper product for food packaging of Comparative Example 8.

[0111] Comparative Example 9

[0112] The difference between the food packaging paper product of Comparative Example 9 and Example 2 lies in the amount of coating in step (3), while the other steps are the same as in Example 2:

[0113] (1) Weigh 70 parts by weight of stearyl alcohol, 14.9 parts by weight of rosin resin, 15 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0114] (2) Mix the stearyl alcohol, rosin resin, carnauba wax and antioxidant weighed in step (1), heat to 105°C, and melt and stir at 105°C for 15 hours to fully melt and mix the components evenly to obtain the coating liquid.

[0115] (3) The coating solution obtained in step (2) is kept at 105°C and hot-melt coated onto the surface of hamburger paper for food packaging, with a coating amount of 3 g / m². 2 .

[0116] (4) After coating, the paper is cooled to room temperature so that the coating liquid forms a coating layer on the surface of the hamburger paper for food packaging, thus obtaining the paper product for food packaging of Comparative Example 9.

[0117] Comparative Example 10

[0118] The difference between the food packaging paper product of Comparative Example 10 and Example 2 is the amount of coating in step (3), while the other steps are the same as in Example 2:

[0119] (1) Weigh 70 parts by weight of stearyl alcohol, 14.9 parts by weight of rosin resin, 15 parts by weight of carnauba wax and 0.1 parts by weight of antioxidant.

[0120] (2) Mix the stearyl alcohol, rosin resin, carnauba wax and antioxidant weighed in step (1), heat to 105°C, and melt and stir at 105°C for 15 hours to fully melt and mix the components evenly to obtain the coating liquid.

[0121] (3) The coating solution obtained in step (2) is kept at 105°C and hot-melt coated onto the surface of hamburger paper for food packaging, with a coating amount of 10 g / m². 2 .

[0122] (4) After coating, the paper is cooled to room temperature so that the coating liquid forms a coating layer on the surface of the hamburger paper for food packaging, thus obtaining the paper product for food packaging of Comparative Example 10.

[0123] The paper products for food packaging prepared in Examples 1-5 and Comparative Examples 1-10 were subjected to performance tests. The test methods and standards are as follows:

[0124] The oil resistance grade test is carried out in accordance with the TAPPI T559 pm standard. Test solutions of different grades are prepared by mixing castor oil, toluene and n-heptane in different proportions. A higher grade indicates a lower surface tension of the test solution and higher test difficulty. During the test, the test solution of the corresponding grade is dropped onto the coated surface of the sample, kept for 15 s, then wiped off, and the paper surface is observed for oil stains; if no oil stain remains on the paper surface, the sample is considered to have passed the test of that grade. The average value of three sets of test data for each group of samples is taken as the oil resistance grade. A higher oil resistance grade indicates better oil resistance of the sample.

[0125] The water contact angle test is performed using the sessile drop method. At normal temperature and pressure, with deionized water as the test medium, a micro-syringe is used to drop a water droplet with a volume of 4-5 μL onto the surface of the wrinkle-free coated area of the test sample. After the droplet shape is stabilized, a contact angle measuring instrument is used to collect the droplet image and calculate the contact angle. Each group of samples is repeatedly tested 5 times at different positions, and the arithmetic mean value is taken as the water contact angle test result after eliminating abnormal values. A larger water contact angle indicates better hydrophobicity of the sample surface.

[0126] The oil contact angle test is performed using the sessile drop method. At normal temperature and pressure, with food-grade vegetable oil as the test medium, a micro-syringe is used to drop an oil droplet with a volume of 4-5 μL onto the surface of the wrinkle-free coated area of the test sample. After the droplet shape is stabilized, a contact angle measuring instrument is used to collect the droplet image and calculate the contact angle. Each group of samples is repeatedly tested 5 times at different positions, and the arithmetic mean value is taken as the oil contact angle test result after eliminating abnormal values. A larger oil contact angle indicates better barrier property of the sample surface to oily media.

[0127] The hot oil resistance performance test is carried out in accordance with PL28-2023 Stain resistance-Hot oil (PL28 test for hot oil resistance / hot oil penetration resistance performance of paper products). Before the test, the test samples are placed in a temperature-controlled laboratory for 24 hours, and 5 samples with flat surfaces and no wrinkles are randomly selected for testing. Place the test sample on a constant temperature plane at 54-57°C with the test surface facing upward; transfer 1-2 mL of canola sunflower oil heated to 80-85°C to the surface of the test sample, and spread it evenly to form a test area with a diameter of no less than 2 cm. After standing for 10 minutes, wipe off the hot oil on the surface with cotton or paper towel and immediately observe the state of the paper surface. When no darkening due to test oil penetration, translucent area or penetrating wet spot appears in the test area, it is judged as qualified; if any of the above phenomena occurs, it is judged as unqualified.

[0128] Dropping point testing was conducted according to ASTM D3954 standard. The wax sample was melted and placed in a standard test cup. After cooling to room temperature, it was placed in a dropping point / softening point tester, and the temperature was increased uniformly at a rate of 1.5℃ / min. The temperature at which the wax sample flowed downwards for 19 mm and the light path was blocked was recorded using a photoelectric detection system and taken as the dropping point. Each group of samples was measured twice in parallel, and the average value was taken as the final test result.

[0129] The dynamic viscosity is tested using the ASTM D3236 standard. The principle is to measure the resistance (torque) experienced by an object (such as a rotor) rotating in a liquid, thereby calculating the liquid's viscosity. A Brookfield viscometer is used in conjunction with a heated bath. The sample is placed in a test tube and kept at a constant temperature in the bath. A rotor of a specific size is immersed in the liquid being tested, and a motor drives the rotor to rotate at a constant speed. The viscous resistance generated by the liquid on the rotor's rotation creates a torque. The instrument measures this torque and, combined with the rotor's geometric parameters and rotational speed, calculates the liquid's dynamic viscosity.

[0130] Oxidation was determined by visual comparison. Coating solutions were prepared according to the formulations and corresponding process conditions of each example and comparative example, and compared with samples obtained by heating the same formulation for 0.5 hours. If the coating solution did not show a significant darkening in color, significant yellowing or browning, turbidity, layering, or a strong oxidizing odor, it was determined to be unoxidized; if the coating solution showed any of the following: a significant darkening in color, turbidity, layering, or a strong oxidizing odor, it was determined to be oxidized.

[0131] Table 1 Performance test results of paper products for food packaging obtained in Examples 1-5 and Comparative Examples 1-10

[0132]

[0133] The water contact angle test diagram of the food packaging paper product prepared in Example 2 is shown below. Figure 2 As shown in the figure, the oil contact angle test diagram is as follows: Figure 3 As shown. By Figure 2 and Figure 3 It can be seen that the water droplets and oil droplets on the surface of the coated waxed paper packaging obtained in Example 2 can maintain a relatively obvious droplet shape on the surface of the coating layer, indicating that the coating layer has good hydrophobicity and oleophobicity, and can provide effective waterproof and oil-proof barrier for the paper substrate.

[0134] As shown in Table 1, the food packaging paper products prepared in Examples 1-5 can all form an effective coating layer on the paper substrate surface and exhibit good waterproof, oil-proof, and heat-resistant oil properties, indicating that the hot-melt coating wax system composed of fatty alcohol, rosin resin, carnauba wax, and antioxidants can form a stable wax barrier structure. Examples 1-3, using different component ratios, all yielded waxed paper packaging with good overall performance, indicating that the composition has a stable layering effect under different ratios. Examples 4 and 5, using behenol and arachidonic acid respectively, still maintained good performance in their waxed paper packaging, indicating that stearyl alcohol, arachidonic acid, and behenol can all be used as fatty alcohol components suitable for the hot-melt coating wax system of this invention.

[0135] By comparing Example 2 with Comparative Examples 1 and 2, it can be seen that the type of fatty alcohol affects the melting state, layering state, and final barrier properties of the coating wax composition. When the fatty alcohol chain length is too short, the coating layer performs poorly in terms of water resistance, oil resistance, and heat resistance; when the fatty alcohol chain length is too long, although a certain surface barrier effect can be formed, the overall applicability in melt processing, spreading flow, and cooling layering is poor. This indicates that selecting a fatty alcohol with an appropriate chain length is beneficial to obtaining a stable hot-melt coating wax system.

[0136] Comparing Examples 1-3 with Comparative Examples 3 and 4 reveals that the component ratio affects the continuity of the coating, its heat-resistant oil properties, and its melt state. When the proportion of fatty alcohol is too low, the coating layer cannot form a sufficiently low surface energy barrier structure; when the proportion of fatty alcohol is too high, the natural plant resin and heat-resistant modifying components are relatively insufficient, affecting the heat-resistant oil properties and melt state of the coating layer. This indicates that fatty alcohol needs to be properly balanced with natural plant resin, heat-resistant modifying components, and antioxidants.

[0137] Comparing Example 2 with Comparative Examples 5 and 6 reveals that natural plant resins and heat-resistant modifying components significantly influence the layering state and hot oil stability of the coated wax system. Insufficient proportion of heat-resistant modifying components reduces the heat-resistant oil stability of the coating layer; insufficient proportion of natural plant resin affects the viscosity and coating state of the molten system, thus impacting the final layering quality. This indicates that natural plant resins and heat-resistant modifying components need to be appropriately combined with fatty alcohols and antioxidants.

[0138] By comparing Example 2 with Comparative Examples 7 and 8, it can be seen that excessively high melt mixing and hot-melt coating temperatures, or excessively long melt mixing times, increase the risk of oxidation of the coating liquid and affect the final barrier properties of the coating layer. This indicates that avoiding excessively high hot-melt processing temperatures and excessively long melt mixing times is beneficial for maintaining the melt flow state of the composition and the stability of the coating layer.

[0139] By comparing Example 2 with Comparative Examples 9 and 10, it can be seen that the coating amount affects the coverage of the paper substrate surface. When the coating amount is too low, the paper substrate surface is not adequately covered, making it difficult to form a continuous and effective coating layer; when the coating amount is too high, the improvement in water and oil resistance tends to be limited, and it may increase the burden on cooling and setting and paper flexibility. This shows that an appropriate coating amount is beneficial for forming a stable coating layer on the paper substrate surface and maintaining the overall application performance of paper-based packaging.

[0140] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A coating layer for the surface of a paper substrate, characterized in that, The coating layer is formed by hot-melt application of a biodegradable coating wax composition onto the surface of a paper substrate, the biodegradable coating wax composition comprising the following components in parts by weight: Fatty alcohols 50-90 parts; 5-25 parts of natural plant resin; 5-25 parts of heat-resistant modifier; Antioxidant 0.05-0.2 parts; The fatty alcohol is selected from one or more of stearyl alcohol, arachidyl alcohol, and behenyl alcohol; The coating layer is formed by heating and melting fatty alcohol, natural plant resin, heat-resistant modifier and antioxidant at 80-110°C to obtain the biodegradable coating wax composition, and then maintaining the biodegradable coating wax composition at 100-110°C and hot-melting it onto the surface of a paper substrate to form the coating layer. The cumulative heating time of the biodegradable coating wax composition during the heating, melting, mixing, and hot-melt coating process is 15-20 hours.

2. A coating layer as described in claim 1, characterized in that, The coating amount of the biodegradable coating wax composition is 5-7 g / m² per unit area of ​​the paper substrate. 2 .

3. A coating layer as described in claim 1, characterized in that, Natural plant resins are selected from one or more of rosin resin, terpene resin, dammar resin, and copal resin.

4. A coating layer as described in claim 1, characterized in that, The heat-resistant modifier is selected from one or both of carnauba wax and hydrogenated castor oil.

5. A coating layer as described in claim 1, characterized in that, The antioxidant is selected from one or both of RIANOX 1010 and RIANOX 1076.

6. A coating layer as described in claim 1, characterized in that, The biodegradable coating wax composition comprises the following components in parts by weight: The composition includes 65-90 parts fatty alcohol, 5-15 parts natural plant resin, 5-15 parts heat-resistant modifier, and 0.08-0.15 parts antioxidant.

7. A coating layer as described in claim 1, characterized in that, The coating has a water contact angle >98° and an oil contact angle >85°.

8. A coating layer as described in claim 1, characterized in that, The biodegradable coating wax composition has a dropping point >72°C and a dynamic viscosity of 10.5-15.0 mPa·s at 100°C.

9. A paper product for food packaging, characterized in that, It includes a paper substrate and a coating layer as described in claim 1, the coating layer being disposed on at least one surface of the paper substrate.

10. A paper product for food packaging as described in claim 9, characterized in that, The paper substrate is hamburger paper, hot dog paper, sandwich wrapping paper, baking wrapping paper, or catering takeaway wrapping paper.

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