Food carton and method of making the same

Abstract

The application provides a food carton paper and a preparation method thereof. The preparation method comprises the following steps: providing raw paper; coating modified polyacrylate water-based paint A on the raw paper to form a heat sealing functional layer; wherein the modified polyacrylate water-based paint A is a polymer emulsion with a core-shell structure; and coating modified polyacrylate water-based paint B on the heat sealing functional layer to form an anti-blocking layer. The food carton paper preparation method provided in the application develops two kinds of modified water-based polyacrylate emulsions, designs a coating structure, and forms a modified polyacrylate film on the surface of the carton paper by using a coating composite method to prepare a food carton packaging paper, so that the food carton paper has a relatively suitable cup-forming heat sealing temperature and the paper blocking is improved.

Description

Technical Field

[0001] The present application relates to the technical field of food paperboard preparation technology, and specifically to a food paperboard and a preparation method thereof. Background Art

[0002] At present, due to the influence of the national plastic ban policy on disposable packaging papers coated with polyethylene, polypropylene, etc., water-based coatings have become an important substitute for coated paper. In recent years, taking water-based coating materials as an example, compared with the traditional PE coating 18g / m2 process, while meeting the barrier performance requirements, water-based coatings only require a coating amount of (5-10) g / m2. The lower coating thickness, on the one hand, reduces the application amount of barrier coating, and on the other hand, the coating is easier to break and degrade. Food packaging paper with water-based coatings has the advantages of saving resources, being repulpable, and recyclable.

[0003] Polyacrylate emulsions, when applied as films, exhibit excellent permeability, high elasticity, biodegradability, acid and chemical resistance, and aging resistance. However, polyacrylate emulsions inherently have drawbacks such as poor water resistance and adhesion, brittleness at low temperatures, and viscosity at high temperatures, which limit their application. Currently, modifications to water-based polyacrylate emulsions have significantly expanded the application range of emulsion coatings.

[0004] Among food packaging paperboards, paper cups, due to their high barrier and processing performance requirements, place even higher demands on the performance and food safety of water-based polyacrylate emulsions. Paperboard coated with water-based polyacrylate emulsions often faces the following application challenges: 1. Excessively high heat-sealing temperatures can lead to loose seals on the cup base, causing leakage when filled with liquid. Heat-sealing temperatures exceed the set temperature of the cup-making machine, and excessively high temperatures (above 400°C) can carbonize and yellow the paper substrate. 2. Moisture absorption can lead to stickiness, causing clumping between the paper sheets during cup production. 3. This high-temperature stickiness can cause the finished cup tube to self-stick in high-temperature and high-humidity conditions, resulting in difficulty removing the cup and damaging the coating's integrity. Achieving low heat-sealing temperatures without re-sticking is difficult with a single polyacrylate emulsion. Adding a certain amount of inorganic filler, such as talc, can improve polyacrylate adhesion. However, the presence of inorganic fillers on the coating surface can still affect the heat-sealing temperature and adhesion strength of the finished cup. Summary of the Invention

[0005] A first aspect of an embodiment of the present application provides a method for preparing food card paper, the method comprising:

[0006] Provide base paper;

[0007] Applying a modified polyacrylate water-based coating A on the base paper to form a heat-sealing functional layer; wherein the modified polyacrylate water-based coating A is a polymer emulsion with a core-shell structure;

[0008] A modified polyacrylate water-based coating B is coated on the heat-sealing functional layer to form an anti-blocking layer.

[0009] In some embodiments, the core of the modified polyacrylate water-based coating A is a polymer of ethylene-butyl acrylate, and the polymerization monomers of the shell structure are ethylene, butyl acrylate, and methyl acrylate.

[0010] In some embodiments, in the ethylene-butyl acrylate polymer, the ratio of ethylene to butyl acrylate is 4-6:6-4; in the polymer monomer of the shell structure, the ratio of ethylene, butyl acrylate and methyl acrylate is 3:5:2.

[0011] In some embodiments, the modified polyacrylate water-based coating B includes methyl methacrylate and butyl acrylate polymerized.

[0012] In some embodiments, the ratio of the methyl methacrylate to the butyl acrylate is 7:3.

[0013] In some embodiments, the modified polyacrylate water-based coating B further includes octadecyl acrylate, and the added amount of octadecyl acrylate is 5-8% of the total amount of the methyl methacrylate and the butyl acrylate.

[0014] In some embodiments, the coating amount of the modified polyacrylate water-based coating A is 8-10 g / m2, and the coating amount of the modified polyacrylate water-based coating B is 0.5-2 g / m2.

[0015] In some embodiments, the thickness of the heat-sealing functional layer is 8-10 μm; the thickness of the anti-adhesion layer is 0.5-2 μm.

[0016] In some embodiments, the preparation method further includes a drying process, wherein the drying process adopts a five-stage hot air oven drying, and the drying temperatures are 110 / 120 / 130 / 110 / 100°C respectively.

[0017] In a second aspect, an embodiment of the present application provides a food cardboard, which is prepared using the preparation method described in the above embodiment.

[0018] The food cardboard preparation method provided in the embodiments of the present application develops two modified water-based polyacrylate emulsions. Through the design of the coating structure, a modified polyacrylate film is formed on the cardboard surface by coating and laminating to produce food card packaging paper. This allows the food cardboard to have a more suitable cup heat sealing temperature while improving paper adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 This is a flow chart of an embodiment of a method for preparing food cardboard of the present application;

[0021] Figure 2 It is a schematic diagram of the structure after a heat-sealing functional layer is formed on the base paper;

[0022] Figure 3 This is a schematic diagram of the stacked structure of an embodiment of the food cardboard of the present application;

[0023] Figure 4 It is a flow chart of another embodiment of the method for preparing food card paper of the present application. DETAILED DESCRIPTION

[0024] The present application will be further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only intended to illustrate the present application and are not intended to limit the scope of the present application. Similarly, the following examples are only some examples of the present application and not all examples. All other examples obtained by those of ordinary skill in the art without creative work are intended to fall within the scope of protection of this application.

[0025] The terms "first", "second" and "third" in the embodiments of the present application are used only for descriptive purposes and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second" and "third" may explicitly or implicitly include at least one of such features. In the description of the present application, "multiple" means at least two, for example, two, three, etc., unless otherwise clearly and specifically defined. All directional indications in the embodiments of the present application (such as up, down, left, right, front, back...) are only used to explain the relative positional relationship, movement, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly. The terms "including" and "having" in the embodiments of the present application and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally also includes steps or units that are not listed, or optionally also includes other steps or components inherent to these processes, methods, products or devices.

[0026] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0027] This application embodiment provides a method for preparing food cardboard, please refer to Figure 1 , Figure 1 1 is a flow chart of an embodiment of a method for preparing food cardboard of the present application, and the preparation method includes but is not limited to the following steps.

[0028] Step S100: providing base paper.

[0029] The base paper used in this embodiment is acid-sized uncoated food card base paper.

[0030] Step S200: coating a modified polyacrylate water-based coating A on the base paper to form a heat-sealing functional layer.

[0031] See also Figure 2 , Figure 2 1 is a schematic diagram of the structure after a heat-sealing functional layer is formed on the base paper, in which 110 is the base paper and 120 is the heat-sealing functional layer.

[0032] Optionally, the modified polyacrylate water-based coating A in this embodiment is a polymer emulsion with a core-shell structure. The core of the modified polyacrylate water-based coating A is a polymer of ethylene-butyl acrylate, and in the polymer of ethylene-butyl acrylate, the ratio of ethylene to butyl acrylate is 4-6:6-4. The polymerized monomers of the shell structure are ethylene, butyl acrylate, and methyl acrylate, and the ratio of ethylene, butyl acrylate, and methyl acrylate is 3:5:2. Soft monomers and hard monomers are polymerized to obtain a suitable glass transition temperature, and the solid content of the modified polyacrylate water-based coating A emulsion is 38-40%. The coating amount of the modified polyacrylate water-based coating A is 8-10 g / m2.

[0033] Please continue reading Figure 1 The preparation method in this embodiment further includes: step S300, coating a modified polyacrylate water-based coating B on the heat-sealing functional layer to form an anti-blocking layer.

[0034] See also Figure 3 , Figure 3 1 is a schematic diagram of the stacked structure of an embodiment of the food card paper of the present application, wherein the anti-adhesion layer 130 is provided on the sealing function layer 120 .

[0035] Wherein, the modified polyacrylate water-based coating B in this embodiment includes methyl methacrylate and butyl acrylate, and the ratio of methyl methacrylate to the butyl acrylate is 7:3. Optionally, the modified polyacrylate water-based coating B may also include octadecyl acrylate, and the addition amount of octadecyl acrylate is 5-8% of the total amount of methyl methacrylate and butyl acrylate. The solid content of the modified polyacrylate water-based coating B emulsion is controlled at about 20%. Wherein, the coating amount of the modified polyacrylate water-based coating B is 0.5-2g / m2. Both coatings (modified polyacrylate water-based coating A and modified polyacrylate water-based coating B) can be applied by scraper coating.

[0036] The two coatings and their coating thicknesses are designed to keep the modified polyacrylate A coating thickness at 8-10μm, offering excellent water and oil barrier properties. The coating's low Tg allows for rapid melting and fluidity during preheating of the cardboard during heat sealing. This allows the molten coating to quickly penetrate the fiber pores on the back of the paperboard during knurling of the paper cup bottom. After knurling, in an unheated environment, the coating temperature drops, allowing it to quickly solidify, providing both bonding and barrier properties. The modified polyacrylate water-based coating B, with a coating thickness of 0.5-2μm, contains long-chain hydrophobic monomers, resulting in excellent water resistance after film formation and resistance to self-adhesion in high-temperature and high-humidity environments. While its melting temperature is slightly higher, the coating thickness is relatively thin, and even melting of Coating A can damage it. Due to the heat-sealing extrusion of the paper cup machine's die, it can penetrate into the fiber pores, minimizing the impact on the heat-sealing temperature.

[0037] The structural characteristics of modified polyacrylate water-based coating A allow its shell structure to partially encapsulate the emulsion seed after demulsification and film formation during the coating process. This can inhibit the self-adhesion of the emulsion seed under high temperature and humidity conditions. This coating also provides good compatibility with modified polyacrylate water-based coating B, ensuring a strong bond between the two coatings. After the cup is filled with hot water, there will be no separation or peeling. During the heat-sealing process for cardboard, the softer seed structure makes the entire coating easy to melt and has good fluidity, resulting in excellent heat-sealing properties. The regular linear structure of the ethylene polymer block in the monomer creates a tight bond between the polymers within the film, resulting in excellent water and oil resistance.

[0038] Modified polyacrylate water-based paint B is modified by adding octadecyl acrylate. The hydrophobic alkyl side chains can make the coating surface have good hydrophobicity. Under high temperature and high humidity, the alkyl side chains will not absorb water vapor and cause adhesion between the two cardboards; it contains the same polymer monomer as water-based paint B, so that the two coatings have good compatibility.

[0039] The food cardboard preparation method provided in the embodiments of the present application develops two modified water-based polyacrylate emulsions. Through the design of the coating structure, a modified polyacrylate film is formed on the cardboard surface by coating and laminating to produce food card packaging paper. This allows the food cardboard to have a more suitable cup heat sealing temperature while improving paper adhesion.

[0040] See also Figure 4 , Figure 4 1 is a flow chart of another embodiment of the method for preparing food card paper of the present application, and the preparation method includes but is not limited to the following steps.

[0041] Step S100: providing base paper.

[0042] The base paper in this embodiment can also be uncoated food card base paper with acid sizing.

[0043] Step S200: coating a modified polyacrylate water-based coating A on the base paper to form a heat-sealing functional layer.

[0044] Optionally, the modified polyacrylate water-based coating A in this embodiment can also be a core-shell structured polymer emulsion. The core of the modified polyacrylate water-based coating A is a polymer of ethylene-butyl acrylate, and in the polymer of ethylene-butyl acrylate, the ratio of ethylene to butyl acrylate is 4-6:6-4. The polymerization monomers of the shell structure are ethylene, butyl acrylate, and methyl acrylate, and the ratio of ethylene, butyl acrylate, and methyl acrylate is 3:5:2. Soft monomers and hard monomers are selected for polymerization to obtain a suitable glass transition temperature, and the solid content of the modified polyacrylate water-based coating A emulsion is 38-40%. The coating amount of the modified polyacrylate water-based coating A is 8-10 g / m2.

[0045] Please continue reading Figure 4 The preparation method in this embodiment further includes: step S300, coating a modified polyacrylate water-based coating B on the heat-sealing functional layer to form an anti-blocking layer.

[0046] Among them, the modified polyacrylate water-based coating B in this embodiment can also be formed by the polymerization of methyl methacrylate and butyl acrylate, and the ratio of methyl methacrylate to the butyl acrylate is 7:3. Optionally, the modified polyacrylate water-based coating B can also include octadecyl acrylate, and the addition amount of octadecyl acrylate is 5-8% of the total amount of methyl methacrylate and butyl acrylate. The solid content of the modified polyacrylate water-based coating B emulsion is controlled at about 20%. Among them, the coating amount of the modified polyacrylate water-based coating B is 0.5-2g / m2. Both coatings (modified polyacrylate water-based coating A and modified polyacrylate water-based coating B) can be applied by scraper coating.

[0047] The two coatings and their coating thicknesses are designed to keep the modified polyacrylate A coating thickness at 8-10μm, offering excellent water and oil barrier properties. The coating's low Tg allows for rapid melting and fluidity during preheating of the cardboard during heat sealing. This allows the molten coating to quickly penetrate the fiber pores on the back of the paperboard during knurling of the paper cup bottom. After knurling, in an unheated environment, the coating temperature drops, allowing it to quickly solidify, providing both bonding and barrier properties. The modified polyacrylate water-based coating B, with a coating thickness of 0.5-2μm, contains long-chain hydrophobic monomers, resulting in excellent water resistance after film formation and resistance to self-adhesion in high-temperature and high-humidity environments. While its melting temperature is slightly higher, the coating thickness is relatively thin, and even melting of Coating A can damage it. Due to the heat-sealing extrusion of the paper cup machine's die, it can penetrate into the fiber pores, minimizing the impact on the heat-sealing temperature.

[0048] The structural characteristics of modified polyacrylate water-based coating A allow its shell structure to partially encapsulate the emulsion seed after demulsification and film formation during the coating process. This can inhibit the self-adhesion of the emulsion seed under high temperature and humidity conditions. This coating also provides good compatibility with modified polyacrylate water-based coating B, ensuring a strong bond between the two coatings. After the cup is filled with hot water, there will be no separation or peeling. During the heat-sealing process for cardboard, the softer seed structure makes the entire coating easy to melt and has good fluidity, resulting in excellent heat-sealing properties. The regular linear structure of the ethylene polymer block in the monomer creates a tight bond between the polymers within the film, resulting in excellent water and oil resistance.

[0049] Modified polyacrylate water-based paint B is modified by adding octadecyl acrylate. The hydrophobic alkyl side chains can make the coating surface have good hydrophobicity. Under high temperature and high humidity, the alkyl side chains will not absorb water vapor and cause adhesion between the two cardboards; it contains the same polymer monomer as water-based paint B, so that the two coatings have good compatibility.

[0050] Please continue reading Figure 4 , different from the above-mentioned embodiment, the preparation method in this embodiment further includes step S400, drying.

[0051] In this step, a five-stage hot air oven drying process can be used, with drying temperatures set at 110 / 120 / 130 / 110 / 100°C. The cold cylinder temperature during winding is controlled at around 40°C. The paperboard exiting the machine is kept below 45°C to prevent the paper roll from sticking due to excessively high winding temperatures.

[0052] The method for preparing food cardboard in the embodiment of the present application is to apply two different functional coatings to form a layer-on-layer structure, so that the paper has a lower heat-sealing bonding temperature and will not be sticky when exposed to moisture or heat, so that the coated food cardboard has a broad application space in the field of food packaging (disposable paper cups, milk tea cups, noodle bowls, etc.). The coated heat-sealed paper has a heat-sealing temperature of 125℃-150℃, 30min COBB≤10g / m2, and an oil-proof grade of 5. After being placed in a constant temperature and humidity chamber at 70℃ and 70% humidity for 24 hours, the adhesion results are 2-4 levels when facing forward and 1-2 levels when facing backward. In addition, a hot coffee penetration test was carried out, and there was no peeling phenomenon on the coated surface (front) after 30 minutes. The two coatings have good compatibility. The specific test results and detection are shown in the following table.

[0053]

[0054]

[0055] The adhesion test standards are shown in the table below.

[0056] Adhesion Rating Almost non-stick (can fall off by itself with a little external force) 1 Slightly sticky but not sticky 2 It feels sticky but it is basically lint-free when pulled apart 3 The feeling of stickiness is strong, and the edges of the round cakes are fuzzy, accounting for less than 20% of the area (originally severe) 4 The raised area accounts for 20%-40% of the round cake area 5 The raised area accounts for 40%-60% of the round cake area 6 The raised area accounts for 60%-80% of the round cake area 7 The raised area accounts for more than 80% of the round cake area 8 Stick together like glue and hard to pull apart 9

[0057] The food paperboard in the examples of this application was developed with two functional water-based coatings based on the barrier and processing requirements of paper cups. This layer-on-layer coating structure imparts excellent barrier properties to the paper cups, achieving a COBB value of less than 10g / m² at 30 minutes and a Kit value of 5. The paperboard remained leak-free for 30 minutes after being filled with coffee. The cupping temperature can be controlled between 330°C and 380°C, making it less prone to sticking in high-temperature and high-humidity conditions. The finished cups are then pulled out smoothly. This solves the problem of a single coating failing to achieve a balanced heat-sealing and adhesion-enhancing effect.

[0058] The above descriptions are only some embodiments of the present application and do not limit the scope of protection of the present application. Any equivalent device or equivalent process transformation made using the contents of the description and drawings of this application, or directly or indirectly applied in other related technical fields, are also included in the scope of patent protection of this application.

Claims

1. A method for preparing food cardboard, characterized in that: The preparation method comprises: Provide base paper; A modified polyacrylate water-based coating A is applied to the base paper to form a heat-sealing functional layer; wherein the modified polyacrylate water-based coating A is a polymer emulsion with a core-shell structure; the core of the modified polyacrylate water-based coating A is an ethylene-butyl acrylate polymer, and the polymerization monomers of the shell structure are ethylene, butyl acrylate, and methyl acrylate; in the ethylene-butyl acrylate polymer, the ratio of ethylene to butyl acrylate is 4-6:6-4; in the polymerization monomers of the shell structure, the ratio of ethylene, butyl acrylate, and methyl acrylate is 3:5:2; A modified polyacrylate water-based coating B is coated on the heat-sealing functional layer to form an anti-blocking layer.

2. The preparation method according to claim 1, characterized in that The modified polyacrylate water-based coating B is formed by polymerization of methyl methacrylate and butyl acrylate.

3. The preparation method according to claim 2, characterized in that The ratio of the methyl methacrylate to the butyl acrylate is 7:

3.

4. The preparation method according to claim 2, characterized in that The modified polyacrylate water-based coating B further comprises octadecyl acrylate, and the added amount of the octadecyl acrylate is 5-8% of the total amount of the methyl methacrylate and the butyl acrylate.

5. The preparation method according to claim 2, characterized in that The coating amount of the modified polyacrylate water-based coating A is 8-10 g / m 2 The coating amount of the modified polyacrylate water-based coating B is 0.5-2g / m 2 .

6. The preparation method according to claim 5, characterized in that The thickness of the heat-sealing functional layer is 8-10 μm; the thickness of the anti-adhesion layer is 0.5-2 μm.

7. The preparation method according to claim 1, characterized in that The preparation method also includes a drying process, wherein the drying process adopts five-stage hot air oven drying, and the drying temperatures are 110 / 120 / 130 / 110 / 100°C respectively.

8. A food paperboard, characterized in that: The food card paper is prepared by the preparation method according to any one of claims 1 to 7.

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