Coated paper for food containers and method for making same

Abstract

This invention provides a coated lunchbox paper, comprising, from top to bottom, a front surface coating, a front intermediate coating, a front pre-coating, a front surface adhesive layer, a surface fiber layer, a core fiber layer, a bottom fiber layer, a back surface adhesive layer, and a back coating. This invention achieves a synergistic effect by adding dispersible rosin and styrene-acrylic surface sizing agent to the coatings of the front pre-coating and back coating, and by adding nano-aluminum sulfate to the front and back surface adhesive layers. This eliminates the need for rosin and aluminum sulfate in the surface and bottom fiber layers, reduces the amount of rosin in the core fiber layer, and eliminates synthetic surface sizing agents in the surface adhesive layer. This solves the problems of poor pulp flow and film formation caused by excessive use of surface starch and synthetic surface sizing agents in the surface adhesive layer, and addresses issues such as poor retention, system contamination, felt contamination, press roll entanglement, and poor interlayer bonding strength caused by excessive wet-end sizing agent usage, ensuring stable paper machine operation and quality.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, and in particular to a coated lunchbox paper and its preparation method. Background Technology

[0002] The Chinese paper tableware industry refers to tableware made from paper, including paper cups, paper boxes (plates), paper dishes, and paper bags. The paper tableware industry has experienced rapid development in the past few years, and its market size and development trends have attracted increasing attention. Currently, paper tableware processing mainly focuses on paper food boxes (plates). With the continued promotion of plastic restriction orders, the market prospects for high-end plastic-free and non-coated paper food boxes (plates) are broad.

[0003] The subsequent processing of coated lunch box (plate) paper involves stamping into boxes (plates), requiring the paper to have a certain interlayer bonding strength, strong water and oil resistance, and strong edge seepage resistance. Currently, the traditional sizing method in the production of coated lunch box (plate) paper in paper mills is in-pulp heavy sizing, which adds a large amount of rosin and aluminum sulfate to the surface fiber layer, core fiber layer, and bottom fiber layer, increases the amount of surface starch in the surface sizing layer, and supplements it with a large amount of styrene-acrylic, propylene-acrylic, or AKD-type synthetic surface sizing agents.

[0004] Adding a large amount of rosin to the fiber layer contaminates the internal system of the paper machine, resulting in poor system retention, contamination of the felt, material entanglement on the press rolls, and high COD in the drainage. At the same time, the addition of a large amount of rosin affects the uniformity of the base paper and the interlayer bonding strength, and the sizing cost is high.

[0005] Excessive addition of surface sizing starch and synthetic surface sizing agents during surface sizing can lead to problems such as poor pulp flow and film formation, resulting in paper defects. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a coated lunch box paper. The coated lunch box paper provided by the present invention has good film-forming properties, good retention, good hot water edge penetration, and good water and oil penetration resistance.

[0007] This invention provides a coated lunch box paper, which, from top to bottom, includes a front surface coating, a front intermediate coating, a front pre-coating, a front surface adhesive layer, a surface fiber layer, a core fiber layer, a bottom fiber layer, a back surface adhesive layer, and a back coating.

[0008] The front pre-coating layer comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.5-0.6 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, 0.02-0.04 parts of sodium hydroxide, 10-15 parts of anionic dispersed rosin gum, and 3-6 parts of anionic styrene-acrylic surface sizing agent.

[0009] Preferably, the front surface coating comprises the following raw materials in parts by weight: 80 parts of 98 grade calcium carbonate, 20 parts of kaolin, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.2-0.3 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, and 0.02-0.04 parts of sodium hydroxide;

[0010] The front intermediate coating comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1 to 0.15 parts of sodium polyacrylate dispersant, 13 to 14 parts of pre-coated SB styrene-butadiene latex, 0.5 to 0.6 parts of CMC, 0.3 to 0.4 parts of potassium zirconium carbonate water-resistant agent, and 0.02 to 0.04 parts of sodium hydroxide.

[0011] Preferably, the back coating comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.5-0.6 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, 0.02-0.04 parts of sodium hydroxide, 10-15 parts of anionic dispersed rosin, and 3-6 parts of anionic styrene-acrylic surface sizing agent.

[0012] Preferably, the front surface adhesive layer comprises the following raw materials in parts by weight: 65-75 parts of surface adhesive oxidized starch and 25-35 parts of nano aluminum sulfate.

[0013] Preferably, the back surface adhesive layer comprises the following raw materials in parts by weight: 65-75 parts of surface adhesive oxidized starch and 25-35 parts of nano aluminum sulfate.

[0014] Preferably, the surface fiber layer contains 30-40 wt% softwood pulp, 60-70 wt% broadwood pulp, and 0.3 kg / t pulp of retention aid.

[0015] Core layer fiber layer needle pulp 0-10wt%, mechanical pulp 90-100wt%, rosin gum dosage 10-15kg / t pulp, iron-free aluminum sulfate dosage 8-15kg / t pulp, retention aid dosage 0.5kg / t pulp, talc powder 50-80kg / t pulp;

[0016] The bottom fiber layer consists of 25-40 wt% softwood pulp and 60-75 wt% broadwood pulp, with a retention aid dosage of 0.3 kg / t pulp.

[0017] Preferably, the ionic styrene-acrylic surface sizing agent has a pH of 5.5-6.5 and a viscosity of <150 mPa·s; the anionic dispersed rosin gum has a particle size of 0.24-0.30 μm and a pH of 4.5-6.5.

[0018] Preferably, the nano-aluminum sulfate has a particle size of 15–25 nm and a specific surface area ≥200 m². 2 / g;

[0019] Preferably, the weight ratio of nano-aluminum sulfate to oven-dried starch in the front surface adhesive layer is 1:3 to 1:4; the weight ratio of nano-aluminum sulfate to oven-dried starch in the back surface adhesive layer is 1:3 to 1:4.

[0020] This invention provides a method for preparing coated lunch box paper according to any one of the above technical solutions, comprising the following steps:

[0021] A) The surface fiber layer raw material, core fiber layer raw material and bottom fiber layer raw material are separately prepared into pulp, compounded, pressed and dried to obtain a composite layer of surface fiber layer-core fiber layer and bottom fiber layer.

[0022] B) Apply adhesive to the upper and lower surfaces of the above composite layer to obtain a front surface adhesive layer and a back surface adhesive layer, respectively.

[0023] C) The front pre-coating material, the front intermediate coating material and the front top coating material are sequentially applied to the adhesive layer on the front surface and dried by infrared drying.

[0024] D) Apply the back coating to the adhesive layer on the back surface, and then dry, calender, and roll it up to obtain the final product.

[0025] Compared with the prior art, the present invention provides a coated lunch box paper, which, from top to bottom, includes a front surface coating layer, a front intermediate coating layer, a front pre-coating layer, a front surface adhesive layer, a surface fiber layer, a core fiber layer, a bottom fiber layer, a back surface adhesive layer, and a back coating layer; the front pre-coating layer includes the following raw materials in parts by weight: 100 parts of 65 grade calcium carbonate, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.5-0.6 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, 0.02-0.04 parts of sodium hydroxide, 10-15 parts of anionic dispersed rosin, and 3-6 parts of anionic styrene-acrylic surface sizing agent. This invention achieves a synergistic effect by adding dispersed rosin and styrene-acrylic surface sizing agent to the pre-coating layer on the front side and adding nano-aluminum sulfate to the surface sizing layer on the front side. This eliminates the need for rosin and aluminum sulfate in the top and bottom fiber layers, reduces the amount of rosin in the core fiber layer, and eliminates the use of synthetic surface sizing agent in the surface sizing layer. This solves the problems of poor pulp flow and film formation caused by excessive use of surface starch and synthetic surface sizing agent in the surface sizing layer. It also solves the problems of poor retention, system contamination, felt contamination, press roll entanglement, and poor interlayer bonding strength caused by excessive use of sizing agent in the wet end pulp, thus ensuring stable paper machine operation and quality. Attached Figure Description

[0026] Figure 1 A schematic diagram of the structure of coated lunchbox paper;

[0027] Figure 2A simplified flowchart of the production process for coating paper lunch boxes. Detailed Implementation

[0028] This invention provides a coated food container paper and its preparation method. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of protection of this invention. The method and application of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the method and application described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0029] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0030] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items.

[0031] This invention provides a method of adding sizing agent to the front pre-coating and back back coating of the coating, adding a certain amount of nano-aluminum sulfate as a fixative to the adhesive layer on the surface of the base paper, discontinuing the use of sizing agent and aluminum sulfate in the surface fiber layer and bottom fiber layer, discontinuing the use of synthetic surface sizing agent in the surface adhesive layer, and adding a portion of sizing agent and aluminum sulfate to the core fiber layer, thereby optimizing the wet end and surface sizing operation mode and achieving the required sizing effect.

[0032] This invention utilizes the addition of anionic dispersed rosin and anionic styrene-acrylic surface sizing agent to the front pre-coating and back coating of coated lunchbox paper, and nano-aluminum sulfate as a fixative to the front and back surface adhesive layers. During coating, moisture in the coating migrates to the surface and interior of the surface adhesive layer and the base paper fiber layer. The moisture wets the surface adhesive layer and the fiber base layer, and the trivalent aluminum ions released from the surface adhesive layer react synergistically with the anionic dispersed rosin and anionic styrene-acrylic surface sizing agent in the front and back pre-coatings, penetrating into the top and bottom fiber layers respectively. They bond with the fibers through directional adhesion, and the sizing is completed by infrared and hot air drying after coating. This eliminates the need for rosin sizing agents and aluminum sulfate fixative in the top and bottom fiber layers, reduces the amount of rosin sizing agent used in the core fiber layer, optimizes the wet end operating environment, reduces COD in the wastewater, and mitigates operational obstacles caused by rosin precipitate from the press section contaminating the felt or causing material entanglement on the press rolls, thereby reducing overall production costs.

[0033] This invention provides a coated lunch box paper, which, from top to bottom, includes a front surface coating, a front intermediate coating, a front pre-coating, a front surface adhesive layer, a surface fiber layer, a core fiber layer, a bottom fiber layer, a back surface adhesive layer, and a back coating.

[0034] The front pre-coating layer comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.5-0.6 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, 0.02-0.04 parts of sodium hydroxide, 10-15 parts of anionic dispersed rosin gum, and 3-6 parts of anionic styrene-acrylic surface sizing agent.

[0035] The coated lunchbox paper provided by this invention includes a front coating.

[0036] In some embodiments of the present invention, the front surface coating comprises the following raw materials in parts by weight: 80 parts of 98 grade calcium carbonate, 20 parts of kaolin, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.2-0.3 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, and 0.02-0.04 parts of sodium hydroxide;

[0037] In some embodiments of the present invention, the front surface coating comprises the following raw materials in parts by weight: 80 parts of 98 grade calcium carbonate, 20 parts of kaolin, 0.11-0.14 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.2-0.3 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, and 0.02-0.04 parts of sodium hydroxide;

[0038] The coated lunchbox paper provided by this invention includes a front intermediate coating layer.

[0039] In some embodiments of the present invention, the front intermediate coating comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1 to 0.15 parts of sodium polyacrylate dispersant, 13 to 14 parts of pre-coated SB styrene-butadiene latex, 0.5 to 0.6 parts of CMC, 0.3 to 0.4 parts of potassium zirconium carbonate water-resistant agent, and 0.02 to 0.04 parts of sodium hydroxide.

[0040] In some embodiments of the present invention, the front intermediate coating comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.11 to 0.14 parts of sodium polyacrylate dispersant, 13 to 14 parts of pre-coated SB styrene-butadiene latex, 0.5 to 0.6 parts of CMC, 0.3 to 0.4 parts of potassium zirconium carbonate water-resistant agent, and 0.02 to 0.04 parts of sodium hydroxide.

[0041] In some embodiments of the present invention, the front pre-coating layer comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1 to 0.15 parts of sodium polyacrylate dispersant, 13 to 14 parts of pre-coated SB styrene-butadiene latex, 0.5 to 0.6 parts of CMC, 0.3 to 0.4 parts of potassium zirconium carbonate water-resistant agent, 0.02 to 0.04 parts of sodium hydroxide, 10 to 15 parts of anionic dispersed rosin, and 3 to 6 parts of anionic styrene-acrylic surface sizing agent.

[0042] According to the present invention, the anionic styrene-acrylic surface sizing agent has a pH of 5.5 to 6.5 and a viscosity of <150 mPa·s.

[0043] The anionic dispersed rosin gum has a particle size of 0.24–0.30 μm, specifically 0.24 μm, 0.25 μm, 0.26 μm, 0.27 μm, 0.28 μm, 0.29 μm, and 0.30 μm. The pH is 4.5–6.5.

[0044] This invention creatively employs anionic styrene-acrylic surface sizing agent and rosin glue to be added to the front pre-coating layer, so that it can form a synergistic effect with the addition of nano aluminum sulfate to the front and back surface adhesive layers, thereby eliminating the use of rosin glue and aluminum sulfate in the surface fiber layer and bottom fiber layer, and reducing the amount of rosin glue used in the core fiber layer.

[0045] The coated lunchbox paper provided by the present invention includes an adhesive layer on the front surface.

[0046] In some embodiments of the present invention, the front surface adhesive layer comprises the following raw materials in parts by weight: 65-75 parts of oxidized starch for surface adhesive and 25-35 parts of nano-aluminum sulfate. After folding, the amount of oxidized starch for surface adhesive is 15-25 kg / t of paper, and the amount of nano-aluminum sulfate is 6-12 kg / t of paper.

[0047] Preferably, the weight ratio of nano-aluminum sulfate to oven-dried starch in the front surface adhesive layer is 1:3 to 1:4.

[0048] Specifically, the nano-aluminum sulfate particles have a particle size of 15–25 nm, specifically 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, or 25 nm; or any value between these two. Specific surface area ≥ 200 m² / g. 2 / g.

[0049] The coated lunchbox paper provided by the present invention includes a surface fiber layer.

[0050] In some embodiments of the present invention, the surface fiber layer contains 30-40 wt% softwood pulp, 60-70 wt% broadwood pulp, and 0.3 kg / t pulp of retention aid.

[0051] In some embodiments of the present invention, the surface fiber layer contains 32-38 wt% softwood pulp, 62-68 wt% broadwood pulp, and 0.3 kg / t pulp of retention aid.

[0052] The coated lunchbox paper provided by the present invention includes a core fiber layer.

[0053] In some embodiments of the present invention, the core fiber layer:

[0054] 0-10 wt% of softwood pulp, 90-100 wt% of mechanical pulp, 10-15 kg / t pulp of rosin gum, 8-15 kg / t pulp of iron-free aluminum sulfate, 0.5 kg / t pulp of retention aid, and 50-80 kg / t pulp of talc.

[0055] In some embodiments of the present invention, the core fiber layer:

[0056] 2-8 wt% of softwood pulp, 92-98 wt% of mechanical pulp, 11-14 kg / t pulp of rosin gum, 11-15 kg / t pulp of iron-free aluminum sulfate, 0.5 kg / t pulp of retention aid, and 52-78 kg / t pulp of talc.

[0057] The coated lunchbox paper provided by the present invention includes a bottom fiber layer.

[0058] In some embodiments of the present invention, the bottom fiber layer consists of 25-40 wt% softwood pulp, 60-75 wt% broadwood pulp, and 0.3 kg / t pulp as a retention aid.

[0059] In some embodiments of the present invention, the bottom fiber layer consists of 26-38 wt% softwood pulp, 62-72 wt% broadwood pulp, and 0.3 kg / t pulp as a retention aid.

[0060] The coated lunch box paper provided by the present invention includes a back surface adhesive layer.

[0061] In some embodiments of the present invention, the back surface adhesive layer comprises the following raw materials in parts by weight: 65-75 parts of oxidized starch for surface adhesive and 25-35 parts of nano-aluminum sulfate. After folding, the amount of oxidized starch for surface adhesive is 15-25 kg / t of paper, and the amount of nano-aluminum sulfate is 6-12 kg / t of paper.

[0062] Specifically, the nano-aluminum sulfate particles have a particle size of 15–25 nm, specifically 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, or 25 nm; or any value between these two. Specific surface area ≥ 200 m² / g. 2 / g.

[0063] Preferably, the weight ratio of nano-aluminum sulfate to oven-dried starch in the adhesive layer on the back surface is 1:3 to 1:4.

[0064] The nano-aluminum sulfate of this invention has a higher specific surface area and better solubility, and can be quickly and evenly dispersed and reacted rapidly. The anionic dispersed rosin latex is fixed on the surface of the top and bottom fiber layers by the positively charged aluminum ions decomposed by the nano-aluminum sulfate. The aluminum sulfate added to the core layer is the traditional iron-free aluminum sulfate.

[0065] The coated lunchbox paper provided by this invention includes a back coating.

[0066] In some embodiments of the present invention, the back coating comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1 to 0.15 parts of sodium polyacrylate dispersant, 13 to 14 parts of pre-coated SB styrene-butadiene latex, 0.5 to 0.6 parts of CMC, 0.3 to 0.4 parts of potassium zirconium carbonate water-resistant agent, 0.02 to 0.04 parts of sodium hydroxide, 10 to 15 parts of anionic dispersed rosin, and 3 to 6 parts of anionic styrene-acrylic surface sizing agent.

[0067] In some embodiments of the present invention, the back coating comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.11-0.14 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.5-0.6 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, 0.02-0.04 parts of sodium hydroxide, 11-14 parts of anionic dispersed rosin, and 3-6 parts of anionic styrene-acrylic surface sizing agent.

[0068] According to the present invention, the anionic styrene-acrylic surface sizing agent has a pH of 5.5 to 6.5 and a viscosity of <150 mPa·s.

[0069] The anionic dispersed rosin gum has a particle size of 0.24–0.30 μm, specifically 0.24 μm, 0.25 μm, 0.26 μm, 0.27 μm, 0.28 μm, 0.29 μm, and 0.30 μm. The pH is 4.5–6.5.

[0070] This invention utilizes the addition of anionic dispersed rosin and anionic styrene-acrylic surface sizing agent to the front pre-coating and back coating of coated lunchbox paper, and nano-aluminum sulfate as a fixative to the front and back surface adhesive layers. During coating, moisture in the coating migrates to the surface and interior of the surface adhesive layer and the base paper fiber layer. The moisture wets the surface adhesive layer and the fiber base layer, and the trivalent aluminum ions released from the surface adhesive layer react synergistically with the anionic dispersed rosin and anionic styrene-acrylic surface sizing agent in the front and back pre-coatings, penetrating into the top and bottom fiber layers respectively. They bond with the fibers through directional adhesion, and the sizing is completed by infrared and hot air drying after coating. This eliminates the need for rosin sizing agents and aluminum sulfate fixative in the top and bottom fiber layers, reduces the amount of rosin sizing agent used in the core fiber layer, optimizes the wet end operating environment, reduces COD in the wastewater, and mitigates operational obstacles caused by rosin precipitate from the press section contaminating the felt or causing material entanglement on the press rolls, thereby reducing overall production costs.

[0071] This invention provides a method for preparing coated lunch box paper according to any one of the above technical solutions, comprising the following steps:

[0072] A) The surface fiber layer raw material, core fiber layer raw material and bottom fiber layer raw material are separately prepared into pulp, compounded, pressed and dried to obtain a composite layer of surface fiber layer-core fiber layer and bottom fiber layer.

[0073] B) Apply adhesive to the upper and lower surfaces of the above composite layer to obtain a front surface adhesive layer and a back surface adhesive layer, respectively.

[0074] C) The front pre-coating material, the front intermediate coating material and the front top coating material are sequentially applied to the adhesive layer on the front surface and dried by infrared drying.

[0075] D) Apply the back coating to the adhesive layer on the back surface, and then dry, calender, and roll it up to obtain the final product.

[0076] The raw materials for the above-mentioned layers have been clearly described above and will not be repeated here.

[0077] The present invention provides a method for preparing coated lunch box paper:

[0078] The raw materials for the surface fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 30-40 wt% softwood pulp, 60-70 wt% hardwood pulp, and 0.3 kg / t of retention aid. The pulp is then fed through the surface layer conveyor, the surface layer headbox, and the surface wire section to obtain the wet surface fiber layer.

[0079] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 0-10 wt%, mechanical pulp 90-100 wt%, rosin glue 10-15 kg / t pulp, iron-free aluminum sulfate 8-15 kg / t pulp, retention aid 0.5 kg / t pulp, and talc powder 50-80 kg / t pulp. After passing through the core layer flow box and the core web section, the wet core fiber layer is obtained.

[0080] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 25-40 wt% softwood pulp, 60-75 wt% hardwood pulp, and 0.3 kg / t pulp retention aid. The pulp is then fed through the bottom headbox and the bottom wire section to obtain the bottom wet fiber layer.

[0081] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0082] Apply adhesive to both the upper and lower surfaces of the composite layer, with an adhesive application rate of 2-4 g / m² on the front side. 2 Apply adhesive to the reverse side at a rate of 2-4 g / m² 2 The front and back adhesive layers are obtained respectively.

[0083] Then it is dried to 93-97% dryness, followed by the coating process.

[0084] Apply the pre-coating material to the adhesive layer on the surface, with a coating amount of 12-15 g / m². 2 Infrared drying to 93-97% dryness.

[0085] Apply the intermediate coating material to the pre-coating layer on the front side, with a coating amount of 7-10 g / m². 2 Infrared drying to 93-97% dryness.

[0086] Apply the pre-coating material to the adhesive layer on the back surface at a coating amount of 12-15 g / m². 2 Infrared drying to 93-97% dryness.

[0087] Apply the topcoat material to the intermediate coat layer, with a coating amount of 11-14 g / m². 2 Infrared drying to 94-92% dryness.

[0088] Then, the product is finished by a calender and wound by a paper winding machine. This invention does not limit the above steps; those skilled in the art can use them as they are known.

[0089] This invention addresses the issues of poor pulp flow and film formation caused by excessive use of surface sizing agents, such as rosin gum dispersing in the front pre-coating and back coatings, styrene-acrylic surface sizing agents, nano-aluminum sulfate in the front and back surface sizing layers, and the discontinuation of rosin gum and aluminum sulfate in the top and bottom fiber layers, as well as the reduction of rosin gum usage in the core fiber layer and the elimination of synthetic surface sizing agents in the surface sizing layer. This solves the problems of poor retention, system contamination, felt contamination, press roll entanglement, and poor interlayer bonding strength caused by excessive use of surface sizing agents in the wet end. It ensures stable paper machine operation and quality. (Note: Adding rosin gum to the fiber layer only ensures 70-90% retention; the unretained portion circulates in the wet end system, and rosin gum decomposes to form contaminants. In coated paper production, the felt and press rolls come into contact with the top and bottom fiber layers; large amounts of rosin gum in the top and bottom fiber layers can lead to felt contamination and rosin gum exudation and entanglement on the press rolls.)

[0090] Adding it to coatings can result in 100% retention, wet-end cleaning, and reduced COD in wastewater, which helps alleviate environmental pressure and wastewater treatment costs.

[0091] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0092] The numerical ranges and parameters involved in this invention have been presented as accurately as possible to the relevant values ​​in the specific embodiments. However, any numerical value inevitably contains standard deviations due to individual test methods. Therefore, unless otherwise expressly stated, it should be understood that all numerical ranges or specific data used in this disclosure may have a reasonable deviation within a certain range, for example, within 1% or 0.5%.

[0093] The embodiments and comparative examples of this invention describe some examples, in which the embodiments illustrate certain implementations of the invention. However, this does not mean that the effects of the invention can only be achieved in these examples.

[0094] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a coated lunchbox paper and its preparation method provided by the present invention.

[0095] Unless otherwise specified, the materials and additives used in the embodiments and comparative examples of this invention are all commercially available.

[0096] Example 1

[0097] The raw materials for the surface fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 30wt% softwood pulp, 70wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the surface layer conveyor, the surface layer headbox, and the surface wire section to obtain the wet surface fiber layer.

[0098] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 3wt%, mechanical pulp 97wt%, rosin glue 10kg / t pulp, iron-free aluminum sulfate 8kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 55kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0099] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 25wt% softwood pulp, 75wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the bottom headbox and the bottom wire section to obtain the bottom wet fiber layer.

[0100] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0101] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an adhesive application rate of 4 g / m² on the front side. 2 The surface adhesive starch was 36 kg / t of paper, the nano aluminum sulfate dosage was 12 kg / t of paper, the reverse side sizing amount was 4 g / m2, and the surface adhesive starch was 36 kg / t of paper, the nano aluminum sulfate dosage was 12 kg / t of paper, and the front and back surface adhesive layers were obtained respectively.

[0102] Then it is dried to 93-97% dryness, followed by the coating process.

[0103] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of anionic dispersed rosin adhesive, and 6 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the above-mentioned front surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0104] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned pre-coating layer, with a coating weight of 7 g / m². 2 Infrared drying to 93-97% dryness forms the front intermediate coating.

[0105] 100 parts of 65-grade calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of anionic dispersed rosin adhesive, and 6 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned back surface adhesive layer at a coating weight of 15 g / m². 2 Infrared drying to 93-97% dryness.

[0106] The front topcoat material, consisting of 80 parts of 98-grade calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at a high speed of 500 rpm for 30 minutes and then applied to the aforementioned front intermediate coating layer, with a coating amount of 11 g / m². 2 Infrared drying to 94-92% dryness.

[0107] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0108] Example 2

[0109] The raw materials for the surface fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 35wt% softwood pulp, 75wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the surface layer conveyor, the surface layer headbox, and the surface wire section to obtain the wet surface fiber layer.

[0110] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 5wt%, mechanical pulp 95wt%, rosin glue 15kg / t pulp, iron-free aluminum sulfate 15kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 60kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0111] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 30wt% softwood pulp, 70wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the bottom headbox and the bottom wire section to obtain the bottom wet fiber layer.

[0112] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0113] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an application rate of 2.7 g / m² on the front side. 2Surface sizing starch dosage: 24 kg / t paper; nano-aluminum sulfate dosage: 6 kg / t paper; reverse side sizing dosage: 2.7 g / m² 2 24 kg / t of surface adhesive starch and 6 kg / t of nano aluminum sulfate were used to obtain the front and back surface adhesive layers, respectively.

[0114] Then it is dried to 93-97% dryness, followed by the coating process.

[0115] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 10 parts of anionic dispersed rosin adhesive, and 5 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the above-mentioned front surface adhesive layer, with a coating amount of 14 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0116] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the pre-coated surface at a coating weight of 8 g / m². 2 Infrared drying to 93-97% dryness forms the front intermediate coating.

[0117] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 10 parts of anionic dispersed rosin adhesive, and 5 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then coated onto the aforementioned back surface adhesive layer, with a coating amount of 14 g / m². 2 Infrared drying to 93-97% dryness.

[0118] The topcoat material, consisting of 80 parts of grade 98 calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned topcoat intermediate layer, with a coating amount of 12 g / m². 2 Infrared drying to 94-92% dryness.

[0119] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0120] Example 3

[0121] The raw material for the surface fiber layer is prepared into pulp. The pulp composition and weight percentage of this layer are 40wt% softwood pulp, 60wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the surface layer conveyor, the surface layer headbox, and the surface mesh section to obtain the wet surface fiber layer.

[0122] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 8wt%, mechanical pulp 92wt%, rosin glue 12kg / t pulp, iron-free aluminum sulfate 10kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 75kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0123] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 40wt% softwood pulp, 60wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the bottom headbox and the bottom wire section to obtain the bottom wet fiber layer.

[0124] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0125] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an application rate of 3.3 g / m² on the front side. 2 The surface sizing agent is 30 kg / t of starch, the nano-aluminum sulfate is 9.5 kg / t of paper, and the reverse side sizing is 3.3 g / m². 2 30 kg / t of starch was used for surface adhesive, and 9.5 kg / t of nano-aluminum sulfate was used to obtain a front surface adhesive layer and a back surface adhesive layer, respectively.

[0126] Then it is dried to 93-97% dryness, followed by the coating process.

[0127] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 13 parts of anionic dispersed rosin adhesive, and 3.5 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the above-mentioned front surface adhesive layer with a coating amount of 12 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0128] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned pre-coating layer on the front side, with a coating amount of 10 g / m². 2 Infrared drying to 93-97% dryness forms the front intermediate coating.

[0129] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 13 parts of anionic dispersed rosin adhesive, and 3.5 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then coated onto the aforementioned back surface adhesive layer, with a coating amount of 12 g / m². 2 Infrared drying to 93-97% dryness.

[0130] The front-side coating material, consisting of 80 parts of 98-grade calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at a high speed of 500 rpm for 30 minutes and then applied to the aforementioned front-side intermediate coating, with a coating amount of 13 g / m². 2 Infrared drying to 94-92% dryness.

[0131] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0132] Comparative Example 1

[0133] The surface fiber layer raw material is prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 30wt%, hardwood pulp 70wt%, retention aid 0.3kg / t pulp, rosin gum 22kg / t pulp, and iron-free aluminum sulfate 20kg / t pulp. After passing through the surface layer flow conveyor, surface layer headbox, and surface mesh section, the surface wet fiber layer is obtained.

[0134] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 3wt%, mechanical pulp 97wt%, rosin glue 30kg / t pulp, iron-free aluminum sulfate 28kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 55kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0135] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 25wt%, hardwood pulp 75wt%, rosin gum 22kg / t pulp, iron-free aluminum sulfate 20kg / t pulp, and retention aid 0.3kg / t pulp. After passing through the bottom flow box, bottom headbox, and bottom mesh section, the bottom wet fiber layer is obtained.

[0136] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0137] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an adhesive application rate of 4 g / m² on the front side. 2 Surface sizing agent dosage: 36 kg / t paper; styrene-acrylic surface sizing agent dosage: 1.5 kg / t paper; reverse side sizing dosage: 4 g / m² 2 36 kg of starch was used per ton of paper for surface adhesive, and 1.5 kg of styrene-acrylic surface sizing agent was used per ton of paper to obtain a front surface adhesive layer and a back surface adhesive layer.

[0138] Then it is dried to 93-97% dryness, followed by the coating process.

[0139] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned front surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0140] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned pre-coating layer, with a coating weight of 7 g / m². 2 Infrared drying to 93-97% dryness forms the front intermediate coating.

[0141] 100 parts of grade 65 calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then coated onto the aforementioned back surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness.

[0142] The front topcoat material, consisting of 80 parts of 98-grade calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at a high speed of 500 rpm for 30 minutes and then applied to the aforementioned front intermediate coating layer, with a coating amount of 11 g / m². 2 Infrared drying to 94-92% dryness.

[0143] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0144] Comparative Example 2

[0145] The surface fiber layer raw material is prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 30wt%, hardwood pulp 70wt%, retention aid 0.3kg / t pulp, rosin gum 20kg / t pulp, and iron-free aluminum sulfate 18kg / t pulp. After passing through the surface layer flow conveyor, surface layer headbox, and surface mesh section, the surface wet fiber layer is obtained.

[0146] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 3wt%, mechanical pulp 97wt%, rosin glue 25kg / t pulp, iron-free aluminum sulfate 22kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 55kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0147] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 25wt%, hardwood pulp 75wt%, rosin gum 20kg / t pulp, iron-free aluminum sulfate 18kg / t pulp, and retention aid 0.3kg / t pulp. After passing through the bottom flow, bottom headbox, and bottom mesh section, the bottom wet fiber layer is obtained.

[0148] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0149] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an adhesive application rate of 4 g / m² on the front side. 2 Surface sizing agent dosage: 36 kg / t paper; styrene-acrylic surface sizing agent dosage: 2.5 kg / t paper; reverse side sizing dosage: 4 g / m² 2 36 kg of starch was used per ton of paper for surface adhesive, and 2.5 kg of styrene-acrylic surface sizing agent was used per ton of paper to obtain a front surface adhesive layer and a back surface adhesive layer.

[0150] Then it is dried to 93-97% dryness, followed by the coating process.

[0151] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned front surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0152] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned pre-coating layer, with a coating weight of 7 g / m². 2 Infrared drying to 93-97% dryness forms the front intermediate coating.

[0153] 100 parts of grade 65 calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then coated onto the aforementioned back surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness.

[0154] The front topcoat material, consisting of 80 parts of 98-grade calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at a high speed of 500 rpm for 30 minutes and then applied to the aforementioned front intermediate coating layer, with a coating amount of 11 g / m². 2 Infrared drying to 94-92% dryness.

[0155] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0156] Comparative Example 3

[0157] The surface fiber layer raw material is prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 30wt%, hardwood pulp 70wt%, retention aid 0.3kg / t pulp, rosin gum 18kg / t pulp, and iron-free aluminum sulfate 16kg / t pulp. After passing through the surface layer flow conveyor, surface layer headbox, and surface mesh section, the surface wet fiber layer is obtained.

[0158] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 3wt%, mechanical pulp 97wt%, rosin glue 20kg / t pulp, iron-free aluminum sulfate 18kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 55kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0159] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 25wt%, hardwood pulp 75wt%, rosin gum 18kg / t pulp, iron-free aluminum sulfate 16kg / t pulp, and retention aid 0.3kg / t pulp. After passing through the bottom flow, bottom headbox, and bottom mesh section, the bottom wet fiber layer is obtained.

[0160] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0161] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an adhesive application rate of 4 g / m² on the front side. 2 Surface sizing agent dosage: 36 kg / t paper; styrene-acrylic surface sizing agent dosage: 2.5 kg / t paper; reverse side sizing dosage: 4 g / m² 2 36 kg of starch was used per ton of paper for surface adhesive, and 2.5 kg of styrene-acrylic surface sizing agent was used per ton of paper to obtain a front surface adhesive layer and a back surface adhesive layer.

[0162] Then it is dried to 93-97% dryness, followed by the coating process.

[0163] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 8 parts of anionic dispersed rosin adhesive, and 0.5 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the above-mentioned front surface adhesive layer with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0164] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned pre-coating layer, with a coating weight of 7 g / m². 2 Infrared drying to 93-97% dryness forms the front intermediate coating.

[0165] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 8 parts of anionic dispersed rosin adhesive, and 0.5 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then coated onto the aforementioned back surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness.

[0166] The front topcoat material, consisting of 80 parts of 98-grade calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at a high speed of 500 rpm for 30 minutes and then applied to the aforementioned front intermediate coating layer, with a coating amount of 11 g / m². 2 Infrared drying to 94-92% dryness.

[0167] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0168] Comparative Example 4

[0169] The raw materials for the surface fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 30wt% softwood pulp, 70wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the surface layer conveyor, the surface layer headbox, and the surface wire section to obtain the wet surface fiber layer.

[0170] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 3wt%, mechanical pulp 97wt%, rosin glue 10kg / t pulp, iron-free aluminum sulfate 8kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 55kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0171] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 25wt% softwood pulp, 75wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the bottom headbox and the bottom wire section to obtain the bottom wet fiber layer.

[0172] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0173] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an adhesive application rate of 4 g / m² on the front side. 2 Surface sizing starch: 36 kg / t paper; iron-free aluminum sulfate: 12 kg / t paper; reverse sizing: 4 g / m²2 36 kg / t of surface adhesive starch and 12 kg / t of iron-free aluminum sulfate were used to obtain the front and back surface adhesive layers, respectively.

[0174] Then it is dried to 93-97% dryness, followed by the coating process.

[0175] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of cationic dispersed rosin, and 6 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the above-mentioned front surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0176] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned pre-coating layer, with a coating weight of 7 g / m². 2 Infrared drying to 93-97% dryness forms the front intermediate coating.

[0177] 100 parts of 65-grade calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of cationic dispersed rosin, and 6 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then coated onto the aforementioned back surface adhesive layer at a coating weight of 15 g / m². 2 Infrared drying to 93-97% dryness.

[0178] The front topcoat material, consisting of 80 parts of 98-grade calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at a high speed of 500 rpm for 30 minutes and then applied to the aforementioned front intermediate coating layer, with a coating amount of 11 g / m². 2 Infrared drying to 94-92% dryness.

[0179] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0180] Comparative Example 5

[0181] The raw materials for the surface fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 30wt% softwood pulp, 70wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the surface layer conveyor, the surface layer headbox, and the surface wire section to obtain the wet surface fiber layer.

[0182] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 3wt%, mechanical pulp 97wt%, rosin glue 10kg / t pulp, iron-free aluminum sulfate 8kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 55kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0183] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 25wt% softwood pulp, 75wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the bottom headbox and the bottom wire section to obtain the bottom wet fiber layer.

[0184] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0185] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an adhesive application rate of 4 g / m² on the front side. 2 Surface sizing starch: 36 kg / t paper; iron-free aluminum sulfate: 12 kg / t paper; reverse sizing: 4 g / m² 2 36 kg / t of surface adhesive starch and 12 kg / t of iron-free aluminum sulfate were used to obtain the front and back surface adhesive layers, respectively.

[0186] Then it is dried to 93-97% dryness, followed by the coating process.

[0187] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of anionic dispersed rosin adhesive, and 6 parts of cationic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the above-mentioned front surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0188] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned pre-coating layer, with a coating weight of 7 g / m². 2Infrared drying to 93-97% dryness forms the front intermediate coating.

[0189] 100 parts of 65-grade calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of anionic dispersed rosin, and 6 parts of cationic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then coated onto the aforementioned back surface adhesive layer at a coating weight of 15 g / m². 2 Infrared drying to 93-97% dryness.

[0190] The front topcoat material, consisting of 80 parts of 98-grade calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at a high speed of 500 rpm for 30 minutes and then applied to the aforementioned front intermediate coating layer, with a coating amount of 11 g / m². 2 Infrared drying to 94-92% dryness.

[0191] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0192] Comparative Example 6

[0193] The raw materials for the surface fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 30wt% softwood pulp, 70wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the surface layer conveyor, the surface layer headbox, and the surface wire section to obtain the wet surface fiber layer.

[0194] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 3wt%, mechanical pulp 97wt%, rosin glue 10kg / t pulp, iron-free aluminum sulfate 8kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 55kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0195] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 25wt% softwood pulp, 75wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the bottom headbox and the bottom wire section to obtain the bottom wet fiber layer.

[0196] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0197] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an adhesive application rate of 4 g / m² on the front side. 2Surface sizing starch: 36 kg / t paper; iron-free aluminum sulfate: 12 kg / t paper; reverse sizing: 4 g / m² 2 36 kg / t of surface adhesive starch and 12 kg / t of iron-free aluminum sulfate were used to obtain the front and back surface adhesive layers, respectively.

[0198] Then it is dried to 93-97% dryness, followed by the coating process.

[0199] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of anionic dispersed rosin adhesive, and 6 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the above-mentioned front surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0200] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned pre-coating layer, with a coating weight of 7 g / m². 2 Infrared drying to 93-97% dryness forms the front intermediate coating.

[0201] 100 parts of 65-grade calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of anionic dispersed rosin adhesive, and 6 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned back surface adhesive layer at a coating weight of 15 g / m². 2 Infrared drying to 93-97% dryness.

[0202] The front topcoat material, consisting of 80 parts of 98-grade calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at a high speed of 500 rpm for 30 minutes and then applied to the aforementioned front intermediate coating layer, with a coating amount of 11 g / m². 2 Infrared drying to 94-92% dryness.

[0203] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0204] Comparative Example 7

[0205] The raw materials for the surface fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 30wt% softwood pulp, 70wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the surface layer conveyor, the surface layer headbox, and the surface wire section to obtain the wet surface fiber layer.

[0206] The core fiber layer raw materials are prepared into pulp. The pulp composition and weight percentage of this layer are: softwood pulp 3wt%, mechanical pulp 97wt%, rosin glue 10kg / t pulp, iron-free aluminum sulfate 8kg / t pulp, retention aid 0.5kg / t pulp, and talc powder 55kg / t pulp. After passing through the core layer flow box, core layer headbox, and core web section, the core wet fiber layer is obtained.

[0207] The raw materials for the bottom fiber layer are prepared into pulp. The pulp composition and weight percentage of this layer are 25wt% softwood pulp, 75wt% hardwood pulp, and 0.3kg / t of retention aid. The pulp is then fed through the bottom headbox and the bottom wire section to obtain the bottom wet fiber layer.

[0208] The above three wet fiber layers are combined, pressed, and dried to obtain a composite layer consisting of a surface fiber layer, a core fiber layer, and a bottom fiber layer.

[0209] Adhesive was applied to both the upper and lower surfaces of the composite layer, with an adhesive application rate of 4 g / m² on the front side. 2 Surface adhesive starch dosage: 36 kg / t paper; polyaluminum chloride dosage: 12 kg / t paper; reverse side adhesive application rate: 4 g / m² 2 36 kg / t of starch was used for surface adhesive, and 12 kg / t of polyaluminum chloride was used for paper to obtain a front surface adhesive layer and a back surface adhesive layer.

[0210] Then it is dried to 93-97% dryness, followed by the coating process.

[0211] 100 parts of 65-grade calcium carbonate pre-coating material, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of anionic dispersed rosin adhesive, and 6 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the above-mentioned front surface adhesive layer, with a coating amount of 15 g / m². 2 Infrared drying to 93-97% dryness forms a front pre-coating.

[0212] 100 parts of grade 65 calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-repellent agent, and 0.03 parts of sodium hydroxide were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned pre-coating layer, with a coating weight of 7 g / m². 2 Infrared drying to 93-97% dryness forms the front intermediate coating.

[0213] 100 parts of 65-grade calcium carbonate, 0.12 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.55 parts of CMC, 0.35 parts of potassium zirconium carbonate water-resistant agent, 0.03 parts of sodium hydroxide, 15 parts of anionic dispersed rosin adhesive, and 6 parts of anionic styrene-acrylic surface sizing agent were uniformly dispersed at 500 rpm for 30 minutes and then applied to the aforementioned back surface adhesive layer at a coating weight of 15 g / m². 2 Infrared drying to 93-97% dryness.

[0214] The front topcoat material, consisting of 80 parts of 98-grade calcium carbonate, 20 parts of kaolin, 0.13 parts of sodium polyacrylate dispersant, 13.5 parts of pre-coated SB styrene-butadiene latex, 0.25 parts of CMC, 0.36 parts of potassium zirconium carbonate water-resistant agent, and 0.028 parts of sodium hydroxide, was uniformly dispersed at a high speed of 500 rpm for 30 minutes and then applied to the aforementioned front intermediate coating layer, with a coating amount of 11 g / m². 2 Infrared drying to 94-92% dryness.

[0215] Then, after finishing with a calender and winding with a paper winding machine, a 270g / m² paper is obtained. 2 Coat the paper plates.

[0216] Table 1: Comparison of test results between experimental cases 1-3 and control groups 1-5:

[0217]

[0218]

[0219] As can be seen from Table 1, the implementation examples 1-3 using the new sizing process have better COBB value control, better control of hot water seepage, better resistance to water and oil penetration, and require less rosin, aluminum sulfate, and styrene-acrylic surface sizing agent, resulting in lower COD in the drainage.

[0220] In Implementation 1, which uses the new sizing process, the materials were replaced with cationic dispersed rosin adhesive, cationic styrene-acrylic surface sizing agent, iron-free aluminum sulfate, and polyaluminum chloride, respectively. The COBB value was controlled, and the hot water seepage was controlled. However, the water and oil penetration resistance was poor and could not achieve the required effect.

[0221] Testing standards:

[0222] ①Cobb testing standard GB / T1540

[0223] COD testing standard: GB11914

[0224] ② Methods for detecting hot water seepage:

[0225] The method for measuring hot water seepage is as follows:

[0226] Cut a 100mm x 100mm sample, measure its thickness (μm), and calculate the average thickness D. Then, completely adhere both sides of the sample with transparent tape and flatten it with a metal roller weighing (10±0.5) kg to measure surface water absorption. Cut a 75mm (longitudinal) x 25mm (transverse) sample from this sample, weigh it G1 (g), and perform a side penetration test. Immerse the prepared sample in distilled water at (95±1)℃ for 10 minutes, remove it, wipe the surface of the sample dry with filter paper, and weigh its wet weight G2 (g).

[0227] Permeability (kg / m 2 )=(G2~G1) / (S*D)*10 6

[0228] In the formula:

[0229] G1: Mass of the sample, in grams (g);

[0230] G2: Wet weight of the soaked sample after wiping the surface dry with filter paper, in grams (g);

[0231] S: Circumference of the sample, in millimeters (mm);

[0232] D – the average thickness of the sample, in micrometers (μm).

[0233] ③ 30-minute water permeability test method:

[0234] The coated paper was used to make a paper box (the inside of the box is the front, and the bottom is the back). A piece of toilet paper was placed on the test table, and the paper box was placed on the toilet paper, ensuring that the toilet paper covered the entire bottom of the paper box. Room temperature water was poured into the box to conduct a leak resistance test. After standing for 30 minutes, the surface showed no peeling or wrinkling, and water leaked out from the bottom and sides. No water seepage points were observed on the toilet paper.

[0235] ④ 30-minute oil penetration resistance test method:

[0236] The coated paper was used to make a box (the inside of the box is the front, and the bottom is the back). A piece of toilet paper was placed on the test table, and the box was placed on the toilet paper, ensuring that the toilet paper covered the entire bottom of the box. Room temperature edible vegetable oil was injected into the box to conduct a leak resistance test. After standing for 30 minutes, the surface showed no peeling or wrinkling, and the bottom and sides showed no oil leakage. No oil seepage points were observed on the toilet paper.

[0237] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A coated lunchbox paper, characterized in that, From top to bottom, it includes the front surface coating, the front intermediate coating, the front pre-coating, the front surface adhesive layer, the surface fiber layer, the core fiber layer, the bottom fiber layer, the back surface adhesive layer, and the back coating. The surface fiber layer consists of 30-40 wt% softwood pulp and 60-70 wt% hardwood pulp, with a retention aid dosage of 0.3 kg / t pulp. Core layer fiber layer needle pulp 0~10 wt%, mechanical pulp 90~100 wt%, rosin gum dosage 10~15 kg / t pulp, iron-free aluminum sulfate dosage 10~15 kg / t pulp, retention aid dosage 0.5 kg / t pulp, talc powder dosage 50~80 kg / t pulp; The bottom fiber layer consists of 25-40 wt% softwood pulp and 60-75 wt% hardwood pulp, with a retention aid dosage of 0.3 kg / t pulp. The front coating comprises the following raw materials in parts by weight: 80 parts of grade 98 calcium carbonate, 20 parts of kaolin, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.2-0.3 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, and 0.02-0.04 parts of sodium hydroxide; The front intermediate coating comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.5-0.6 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, and 0.02-0.04 parts of sodium hydroxide; The back coating comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.5-0.6 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, 0.02-0.04 parts of sodium hydroxide, 10-15 parts of anionic dispersed rosin, and 3-6 parts of anionic styrene-acrylic surface sizing agent; The front pre-coating comprises the following raw materials in parts by weight: 100 parts of grade 65 calcium carbonate, 0.1-0.15 parts of sodium polyacrylate dispersant, 13-14 parts of pre-coated SB styrene-butadiene latex, 0.5-0.6 parts of CMC, 0.3-0.4 parts of potassium zirconium carbonate water-resistant agent, 0.02-0.04 parts of sodium hydroxide, 10-15 parts of anionic dispersed rosin gum, and 3-6 parts of anionic styrene-acrylic surface sizing agent; The front surface adhesive layer comprises the following raw materials in parts by weight: 65-75 parts of surface adhesive oxidized starch, and 25-35 parts of nano aluminum sulfate; The back surface adhesive layer comprises the following raw materials in parts by weight: 65-75 parts of surface adhesive oxidized starch and 25-35 parts of nano aluminum sulfate.

2. The coated lunchbox paper according to claim 1, characterized in that, The ion-styrene-acrylic surface sizing agent has a pH of 5.5-6.5 and a viscosity of <150 mPa·s; The anionic dispersed rosin gum has a particle size of 0.24~0.30μm and a pH of 4.5~6.

5.

3. The coated lunchbox paper according to claim 1, characterized in that, The nano-aluminum sulfate has a particle size of 15~25nm and a specific surface area ≥200m². 2 / g.

4. The coated lunchbox paper according to claim 1, characterized in that, The weight ratio of nano-aluminum sulfate to oven-dried starch in the front surface adhesive layer is 1:3 to 1:4; the weight ratio of nano-aluminum sulfate to oven-dried starch in the back surface adhesive layer is 1:3 to 1:

4.

5. A method for preparing coated lunchbox paper according to any one of claims 1 to 4, characterized in that, Includes the following steps: A) The surface fiber layer raw material, core fiber layer raw material and bottom fiber layer raw material are separately prepared into pulp, compounded, pressed and dried to obtain a composite layer of surface fiber layer-core fiber layer and bottom fiber layer. B) Apply adhesive to the upper and lower surfaces of the above composite layer to obtain a front surface adhesive layer and a back surface adhesive layer, respectively. C) The front pre-coating material, the front intermediate coating material and the front top coating material are sequentially applied to the adhesive layer on the front surface and dried by infrared drying. D) Apply the back coating to the adhesive layer on the back surface, and then dry, calender, and roll it up to obtain the final product.

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