Moisture-proof high-strength corrugated paperboard and preparation method thereof

Abstract

The present application relates to a kind of moisture-proof high-strength corrugated paperboard and its preparation method, belong to packaging material technical field.The paperboard is by surface layer, first corrugated layer, intermediate flat layer, second corrugated layer and inner layer sequentially composite;First corrugated layer is A type corrugation, and the height of herringbone is 4.5-5.5 mm;Second corrugated layer is B type corrugation, and the height of herringbone is 2.5-3.2 mm;Surface layer and inner layer surface are coated with waste protein-based modified sizing agent layer.Preparation method includes: preparation waste protein-based modified sizing agent and biomass adhesive;Each layer base paper is compounded by biomass adhesive, and paperboard blank is obtained by drying under negative pressure;Again, surface sizing, drying are obtained.The present application is by "A herringbone, flat layer, B herringbone" I-shaped steel structure design, in combination with waste protein resource utilization of environmental protection sizing agent, and low-temperature negative pressure compounding process, so that paperboard has excellent moisture-proof performance and high-strength characteristics, simultaneously realizes clean production.

Description

Technical Field

[0001] This invention belongs to the field of packaging materials technology, and relates to a moisture-proof high-strength corrugated cardboard and its preparation method. Background Technology

[0002] Corrugated cardboard, due to its lightweight, low cost, and recyclability, is widely used in the transport packaging of various products and is one of the most widely used environmentally friendly packaging materials in the packaging industry. Its conventional manufacturing process mainly includes steps such as base paper pretreatment, corrugation forming, interlayer bonding, pressing and drying, and cutting. The core principle is to enhance the cardboard's compression and impact resistance through the supporting effect of the corrugated structure, and to ensure the bonding strength between the layers through the adhesive. However, traditional corrugated cardboard has two inherent defects: first, poor moisture resistance, easily absorbing moisture and softening in humid environments, leading to a sharp decrease in compressive strength and affecting the packaging's protective effect; second, insufficient strength, making it difficult to meet the needs of heavy-duty packaging or long-term storage, thus limiting its application range.

[0003] To address the aforementioned issues, existing technologies primarily employ three approaches: First, coating the cardboard surface with plastic or synthetic polymer sizing agents (such as acrylates and polyurethanes) to form a waterproof membrane and improve moisture resistance. However, this approach increases the difficulty of cardboard recycling, and synthetic polymers are difficult to degrade, failing to meet the requirements of green and environmentally friendly development. Second, increasing the basis weight of the base paper or using high-strength base paper to improve mechanical properties. However, this significantly increases raw material costs and cardboard weight, while also leading to increased transportation energy consumption, contradicting the trend towards lightweight packaging. Third, employing multi-layer composite structures. However, these structures often only increase strength by adding more layers, lacking targeted structural optimization, and the interlayer adhesion still relies on traditional starch adhesives, resulting in poor water resistance and difficulty in achieving a synergistic improvement in both moisture resistance and high strength. Furthermore, some technologies, by adding reinforcing components such as nanoparticles to the adhesive, can improve bonding strength to some extent, but fail to address the core pain point of insufficient environmental friendliness.

[0004] More significantly, existing improvement solutions not only fail to simultaneously meet the triple requirements of moisture resistance, high strength, and environmental protection, but also fail to effectively utilize industrial waste resources. my country generates a large amount of waste protein resources annually, such as chromium-containing leather scraps from the leather industry and waste feathers from the livestock and poultry processing industry. If these wastes are disposed of through landfill or incineration, it not only wastes valuable resources but also causes environmental pollution. Furthermore, the moisture-proof coatings and adhesives of existing corrugated cardboard still largely rely on synthetic materials, posing environmental risks and failing to achieve resource utilization of waste resources. Therefore, how to utilize waste protein resources and develop environmentally friendly corrugated cardboard with both moisture resistance and high strength, solving the problems of poor environmental performance, resource waste, and uneven performance in existing technologies, has become an urgent technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a moisture-proof high-strength corrugated cardboard and its preparation method, aiming to solve the technical problems of existing corrugated cardboard which is difficult to balance moisture resistance and strength, has high energy consumption in preparation process, and wastes waste protein resources. The invention provides a moisture-proof high-strength corrugated cardboard with optimized structure, environmentally friendly materials, and energy-saving process, as well as its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions: A moisture-proof and high-strength corrugated cardboard is composed of a surface layer, a first corrugated layer, an intermediate flat-pressed layer, a second corrugated layer, and an inner layer, which are sequentially laminated together. The first corrugated layer is type A corrugated, with a corrugation height of 4.5-5.5 mm; The second corrugated layer is a type B corrugated layer with a corrugation height of 2.5-3.2 mm; Both the surface of the top layer and the inner layer are coated with a waste protein-based modified sizing agent layer.

[0007] This invention employs a composite structure of "A-type corrugated board, intermediate flat-pressed layer, and B-type corrugated board." Its reinforcement mechanism is similar to that of "I-beams" or "sandwich panels" in engineering structures. The A-type corrugated board has a larger flute height (4.5-5.5 mm) and fewer flutes per unit length, primarily bearing longitudinal loads along the flute direction, providing higher edge crush strength and bending stiffness. The B-type corrugated board has a smaller flute height (2.5-3.2 mm) and more flutes per unit length, primarily bearing transverse loads, improving the planar compressive strength and cushioning performance of the cardboard. The intermediate flat-pressed layer, located between the two flute layers, acts as a "web." When the cardboard is subjected to vertical pressure, the intermediate flat-pressed layer connects the upper and lower flute layers into a whole, effectively transferring and dispersing stress, preventing flute buckling and instability, thereby significantly improving overall compressive strength. Simultaneously, the flat-pressed layer itself has a certain stiffness, increasing the cardboard's thickness and moment of inertia, thus greatly improving bending stiffness.

[0008] Surface sizing agents are prepared from waste proteins. The waste proteins are moderately hydrolyzed under alkaline conditions, reducing their molecular weight to 1000-5000 Da, exposing more active groups (amino, carboxyl, and hydroxyl groups). Simultaneously, the reduced molecular size facilitates subsequent modification reactions and penetration into the paper fibers. Silane coupling agents are used to graft and modify the protein molecules. The alkoxy group at one end of the silane hydrolyzes and reacts with the hydroxyl or amino groups of the protein molecules to form covalent bonds, while the long-chain alkyl or vinyl group at the other end imparts hydrophobicity to the protein. The modified protein molecules possess both hydrophilic groups (which can bind to the fiber) and hydrophobic groups (facing outwards), forming a directionally arranged "hydrophobic barrier" on the fiber surface. Further cross-linking with epichlorohydrin creates a three-dimensional network structure between the protein molecules, improving the density and water resistance of the sizing film. The cross-linked film is more robust and less soluble in water. After the sizing agent is applied to the surface of the paperboard, the modified protein molecules penetrate into the fiber pores. Their active groups form hydrogen bonds and covalent bonds with the hydroxyl groups on the fiber surface, firmly bonding the fibers and filling the capillary channels between them. After drying, a continuous, dense, hydrophobic film forms on the paperboard surface, effectively blocking the penetration of liquid and gaseous water and significantly improving surface strength and burst resistance. This sizing agent transforms waste protein resources into high-value-added functional materials and is completely biodegradable, meeting environmental and clean production requirements.

[0009] As a preferred embodiment of the present invention, the surface layer and the first corrugated layer, the first corrugated layer and the intermediate flat layer, the intermediate flat layer and the second corrugated layer, and the second corrugated layer and the inner layer are bonded together by a biomass adhesive. The biomass adhesive comprises the following components in parts by weight: 100 parts starch, 20-30 parts plant protein, 3-8 parts nano-montmorillonite, and 1-2 parts borax.

[0010] Furthermore, a method for preparing the aforementioned moisture-proof high-strength corrugated cardboard includes the following steps: (1) Preparation of waste protein-based modified sizing agent: Hydrolyze waste protein raw materials to obtain protein hydrolysate; add hydrophobic modifier to protein hydrolysate and react to obtain modified protein solution; mix modified protein solution with adhesive to prepare surface sizing solution; (2) Preparation of biomass adhesive: Mix starch, plant protein, nano-montmorillonite, borax and water, and gelatinize at 40-55℃ to obtain biomass adhesive; (3) Lamination: The face paper, the first corrugated base paper, the middle flat-pressed base paper, the second corrugated base paper, and the liner paper are laminated on a laminating machine using the biomass adhesive obtained in step (2), and dried under negative pressure to obtain a paperboard blank; (4) Surface sizing: The surface sizing liquid obtained in step (1) is applied to the surface of the outer and inner layers of the cardboard blank obtained in step (3), and dried to obtain the final product.

[0011] As a preferred technical solution of the present invention, the waste protein raw material in step (1) is at least one of waste feathers and leather scraps; the hydrolysis is alkaline hydrolysis, and the hydrolysis conditions are: alkaline aqueous solution concentration 0.1-1.0 wt%, temperature 70-95℃, time 2-4 hours.

[0012] As a preferred technical solution of the present invention, the hydrophobic modifier in step (1) is at least one of vinyltrimethoxysilane and vinyltriethoxysilane; the amount of hydrophobic modifier is 5-15% of the dry weight of the protein.

[0013] As a preferred technical solution of the present invention, step (1) further includes a crosslinking modification step: adding a crosslinking agent to the modified protein solution and reacting it for 1-3 hours at 40-60℃ and pH 8-10 to obtain a crosslinked-modified protein solution; the crosslinking agent is epichlorohydrin, and the amount used is 3-8% of the dry weight of the protein.

[0014] As a preferred technical solution of the present invention, the solid content of the biomass adhesive in step (2) is 20-25%, the viscosity is 3000-5000 mPa·s, and the gelatinization temperature is 45-50℃.

[0015] As a preferred technical solution of the present invention, the negative pressure of the negative pressure drying in step (3) is -0.03 to -0.06 MPa, the drying temperature is 70-90℃, and the drying time is 3-5 minutes.

[0016] As a preferred embodiment of the present invention, the coating amount in step (4) is 5-8 g / m². 2 The drying temperature is 80-100℃.

[0017] As a preferred embodiment of the present invention, the basis weight of the face paper is 150-200 g / m². 2 The basis weight of the inner paper is 120-150 g / m². 2 The basis weight of the first corrugated base paper is 120-150 g / m². 2 The basis weight of the second corrugated base paper is 100-120 g / m². 2 The quantitative density of the intermediate flat layer is 80-100 g / m³. 2 .

[0018] The beneficial effects of this invention are: (1) This invention adopts a composite structure of “A-type corrugated board, intermediate flat pressing layer, and B-type corrugated board”. The A-type corrugated board (flute height 4.5-5.5 mm) mainly bears the longitudinal load, providing high edge crush strength and bending stiffness; the B-type corrugated board (flute height 2.5-3.2 mm) mainly bears the transverse load, improving the planar compressive strength and buffering performance; the intermediate flat pressing layer is located between the two corrugated boards, acting as a “web” to connect the upper and lower corrugated boards into a whole, effectively transferring and dispersing stress, and preventing corrugated board buckling. The synergistic effect of the three improves the mechanical properties of the cardboard, such as edge crush strength, bursting strength, and puncture strength, meeting the stringent strength requirements of heavy-duty packaging.

[0019] (2) This invention utilizes industrial solid waste such as waste feathers and leather scraps to prepare surface sizing agents, achieving "turning waste into treasure". After moderate alkaline hydrolysis, the molecular weight of waste protein is reduced to 1000-5000 Da, exposing more active groups, which is beneficial for subsequent modification and penetration into the fiber interior. Silane coupling agents are used for hydrophobic modification, allowing hydrophobic groups to be grafted onto the protein molecules, which are then cross-linked with epichlorohydrin to form a three-dimensional network structure. After the modified sizing agent is coated on the paperboard surface, the active groups are firmly bonded to the fibers, and the hydrophobic groups form a directional "hydrophobic barrier" facing outwards, while filling the capillary channels between fibers to form a continuous, dense, and hydrophobic film. This sizing agent enables the paperboard surface contact angle to reach over 100°, and the edge crush strength retention rate is ≥85% under high humidity environment (RH90%, 24 h), solving the industry problem of traditional corrugated paperboard softening and sudden strength drop when exposed to moisture.

[0020] (3) This invention uses a starch-plant protein-nano-montmorillonite composite biomass adhesive. The addition of plant protein lowers the gelatinization temperature to 45-50℃, saving more than 30% energy compared to traditional starch adhesives, while avoiding damage to fiber strength from high temperatures; the layered structure of nano-montmorillonite forms a "zigzag path," significantly improving the moisture resistance of the adhesive layer; borax, as a crosslinking agent, increases initial tack and cohesion. This adhesive releases no formaldehyde, has high bonding strength, and maintains excellent bonding performance even in high humidity environments, ensuring that the multilayer structure does not delaminate during long-term use. Detailed Implementation

[0021] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below. Example 1

[0022] A moisture-proof and high-strength corrugated cardboard is composed of a surface layer, a first corrugated layer, an intermediate flat-pressed layer, a second corrugated layer, and an inner layer, which are sequentially laminated together. The first corrugated layer is a type A corrugated layer with a corrugation height of 5.0 mm; The second corrugated layer is a type B corrugated layer with a corrugation height of 3.0 mm; Both the surface of the top layer and the inner layer are coated with a waste protein-based modified sizing agent layer.

[0023] The surface layer and the first corrugated layer, the first corrugated layer and the intermediate flat layer, the intermediate flat layer and the second corrugated layer, and the second corrugated layer and the inner layer are bonded together by biomass adhesive. The biomass adhesive comprises the following components in parts by weight: 100 parts starch, 25 parts plant protein, 5 parts nano-montmorillonite, and 1.5 parts borax.

[0024] A method for preparing the aforementioned moisture-proof high-strength corrugated cardboard includes the following steps: (1) Preparation of waste protein-based modified sizing agent: Hydrolyze waste protein raw materials to obtain protein hydrolysate; add hydrophobic modifier to protein hydrolysate and react to obtain modified protein solution; mix modified protein solution with adhesive to prepare surface sizing solution; (2) Preparation of biomass adhesive: Mix starch, soybean protein, nano-montmorillonite, borax and water, and gelatinize at 50°C to obtain biomass adhesive; (3) Lamination: The face paper, the first corrugated base paper, the middle flat-pressed base paper, the second corrugated base paper, and the liner paper are laminated on a laminating machine using the biomass adhesive obtained in step (2), and dried under negative pressure to obtain a paperboard blank; (4) Surface sizing: The surface sizing liquid obtained in step (1) is applied to the surface of the outer and inner layers of the cardboard blank obtained in step (3), and dried to obtain the final product.

[0025] The waste protein raw material mentioned in step (1) is waste feathers; the hydrolysis is alkaline hydrolysis, and the hydrolysis conditions are: sodium hydroxide solution concentration 0.5 wt%, temperature 80℃, time 3 hours.

[0026] The hydrophobic modifier mentioned in step (1) is vinyltrimethoxysilane; the amount of hydrophobic modifier used is 10% of the dry protein mass.

[0027] Step (1) also includes a crosslinking modification step: a crosslinking agent is added to the modified protein solution, and the reaction is carried out at 50°C and pH 9 for 2 hours to obtain a crosslinked-modified protein solution; the crosslinking agent is epichlorohydrin, and the amount used is 5% of the dry weight of the protein.

[0028] The biomass adhesive in step (2) has a solid content of 22% and a viscosity of 4000 mPa·s; the gelatinization temperature is 48℃.

[0029] The negative pressure of the negative pressure drying in step (3) is -0.05 MPa, the drying temperature is 80℃, and the drying time is 4 minutes.

[0030] The coating amount mentioned in step (4) is 6 g / m 2 The drying temperature is 90℃.

[0031] The basis weight of the facial tissue is 180 g / m³. 2 The basis weight of the inner paper is 140 g / m². 2 The basis weight of the first corrugated base paper is 140 g / m². 2 The basis weight of the second corrugated base paper is 110 g / m². 2 The quantitative amount of the intermediate flat layer is 90 g / m 2 . Example 2

[0032] A moisture-proof and high-strength corrugated cardboard is composed of a surface layer, a first corrugated layer, an intermediate flat-pressed layer, a second corrugated layer, and an inner layer, which are sequentially laminated together. The first corrugated layer is a type A corrugated layer with a corrugation height of 5.0 mm; The second corrugated layer is a type B corrugated layer with a corrugation height of 3.0 mm; Both the surface of the top layer and the inner layer are coated with a waste protein-based modified sizing agent layer.

[0033] The surface layer and the first corrugated layer, the first corrugated layer and the intermediate flat layer, the intermediate flat layer and the second corrugated layer, and the second corrugated layer and the inner layer are bonded together by biomass adhesive. The biomass adhesive comprises the following components in parts by weight: 100 parts starch, 25 parts plant protein, 5 parts nano-montmorillonite, and 1.5 parts borax.

[0034] A method for preparing the aforementioned moisture-proof high-strength corrugated cardboard includes the following steps: (1) Preparation of waste protein-based modified sizing agent: Hydrolyze waste protein raw materials to obtain protein hydrolysate; add hydrophobic modifier to protein hydrolysate and react to obtain modified protein solution; mix modified protein solution with adhesive to prepare surface sizing solution; (2) Preparation of biomass adhesive: Mix starch, soybean protein, nano-montmorillonite, borax and water, and gelatinize at 50°C to obtain biomass adhesive; (3) Lamination: The face paper, the first corrugated base paper, the middle flat-pressed base paper, the second corrugated base paper, and the liner paper are laminated on a laminating machine using the biomass adhesive obtained in step (2), and dried under negative pressure to obtain a paperboard blank; (4) Surface sizing: The surface sizing liquid obtained in step (1) is applied to the surface of the outer and inner layers of the cardboard blank obtained in step (3), and dried to obtain the final product.

[0035] The waste protein raw material mentioned in step (1) is waste leather scraps from leather tanning; the hydrolysis is alkaline hydrolysis, and the hydrolysis conditions are: soaking in 0.1 mol / L oxalic acid for 2 hours, washing with water until neutral for dechromium removal pretreatment, and then soaking in 0.5 wt% sodium hydroxide solution at 80°C for 3 hours.

[0036] The hydrophobic modifier mentioned in step (1) is vinyltrimethoxysilane; the amount of hydrophobic modifier used is 10% of the dry protein mass.

[0037] Step (1) also includes a crosslinking modification step: a crosslinking agent is added to the modified protein solution, and the reaction is carried out at 50°C and pH 9 for 2 hours to obtain a crosslinked-modified protein solution; the crosslinking agent is epichlorohydrin, and the amount used is 5% of the dry weight of the protein.

[0038] The biomass adhesive in step (2) has a solid content of 22% and a viscosity of 4000 mPa·s; the gelatinization temperature is 48℃.

[0039] The negative pressure of the negative pressure drying in step (3) is -0.05 MPa, the drying temperature is 80℃, and the drying time is 4 minutes.

[0040] The coating amount mentioned in step (4) is 6 g / m 2 The drying temperature is 90℃.

[0041] The basis weight of the facial tissue is 180 g / m³. 2 The basis weight of the inner paper is 140 g / m². 2 The basis weight of the first corrugated base paper is 140 g / m². 2 The basis weight of the second corrugated base paper is 110 g / m². 2 The quantitative amount of the intermediate flat layer is 90 g / m 2 . Example 3

[0042] A moisture-proof and high-strength corrugated cardboard is composed of a surface layer, a first corrugated layer, an intermediate flat-pressed layer, a second corrugated layer, and an inner layer, which are sequentially laminated together. The first corrugated layer is a type A corrugated layer with a corrugation height of 4.5 mm; The second corrugated layer is a type B corrugated layer with a corrugation height of 2.5 mm; Both the surface of the top layer and the inner layer are coated with a waste protein-based modified sizing agent layer.

[0043] The surface layer and the first corrugated layer, the first corrugated layer and the intermediate flat layer, the intermediate flat layer and the second corrugated layer, and the second corrugated layer and the inner layer are bonded together by biomass adhesive. The biomass adhesive comprises the following components in parts by weight: 100 parts starch, 20 parts soybean protein, 3 parts nano-montmorillonite, and 1 part borax.

[0044] A method for preparing the aforementioned moisture-proof high-strength corrugated cardboard includes the following steps: (1) Preparation of waste protein-based modified sizing agent: Hydrolyze waste protein raw materials to obtain protein hydrolysate; add hydrophobic modifier to protein hydrolysate and react to obtain modified protein solution; mix modified protein solution with adhesive to prepare surface sizing solution; (2) Preparation of biomass adhesive: Mix starch, plant protein, nano-montmorillonite, borax and water, and gelatinize at 40°C to obtain biomass adhesive; (3) Lamination: The face paper, the first corrugated base paper, the middle flat-pressed base paper, the second corrugated base paper, and the liner paper are laminated on a laminating machine using the biomass adhesive obtained in step (2), and dried under negative pressure to obtain a paperboard blank; (4) Surface sizing: The surface sizing liquid obtained in step (1) is applied to the surface of the outer and inner layers of the cardboard blank obtained in step (3), and dried to obtain the final product.

[0045] The waste protein raw material mentioned in step (1) is waste feathers; the hydrolysis is alkaline hydrolysis, and the hydrolysis conditions are: alkaline aqueous solution concentration 0.3 wt%, temperature 70℃, time 2 hours.

[0046] The hydrophobic modifier mentioned in step (1) is vinyltriethoxysilane; the amount of hydrophobic modifier used is 5% of the dry protein mass.

[0047] Step (1) also includes a crosslinking modification step: a crosslinking agent is added to the modified protein solution, and the reaction is carried out at 40°C and pH 8 for 1 hour to obtain a crosslinked-modified protein solution; the crosslinking agent is epichlorohydrin, and the amount used is 3% of the dry weight of the protein.

[0048] The biomass adhesive in step (2) has a solid content of 20% and a viscosity of 3000 mPa·s; the gelatinization temperature is 45℃.

[0049] The negative pressure of the negative pressure drying in step (3) is -0.03MPa, the drying temperature is 70℃, and the drying time is 3 minutes.

[0050] The coating amount mentioned in step (4) is 5 g / m 2 The drying temperature is 80℃.

[0051] The basis weight of the facial tissue is 150 g / m². 2 The basis weight of the inner paper is 120 g / m². 2 The basis weight of the first corrugated base paper is 120 g / m². 2The basis weight of the second corrugated base paper is 100 g / m². 2 The quantitative amount of the intermediate flat layer is 80 g / m. 2 . Example 4

[0052] A moisture-proof and high-strength corrugated cardboard is composed of a surface layer, a first corrugated layer, an intermediate flat-pressed layer, a second corrugated layer, and an inner layer, which are sequentially laminated together. The first corrugated layer is a type A corrugated layer with a corrugation height of 5.5 mm; The second corrugated layer is a type B corrugated layer with a corrugation height of 3.2 mm; Both the surface of the top layer and the inner layer are coated with a waste protein-based modified sizing agent layer.

[0053] The surface layer and the first corrugated layer, the first corrugated layer and the intermediate flat layer, the intermediate flat layer and the second corrugated layer, and the second corrugated layer and the inner layer are bonded together by biomass adhesive. The biomass adhesive comprises the following components in parts by weight: 100 parts starch, 30 parts plant protein, 8 parts nano-montmorillonite, and 2 parts borax.

[0054] A method for preparing the aforementioned moisture-proof high-strength corrugated cardboard includes the following steps: (1) Preparation of waste protein-based modified sizing agent: Hydrolyze waste protein raw materials to obtain protein hydrolysate; add hydrophobic modifier to protein hydrolysate and react to obtain modified protein solution; mix modified protein solution with adhesive to prepare surface sizing solution; (2) Preparation of biomass adhesive: Mix starch, soybean protein, nano-montmorillonite, borax and water, and gelatinize at 55°C to obtain biomass adhesive; (3) Lamination: The face paper, the first corrugated base paper, the middle flat-pressed base paper, the second corrugated base paper, and the liner paper are laminated on a laminating machine using the biomass adhesive obtained in step (2), and dried under negative pressure to obtain a paperboard blank; (4) Surface sizing: The surface sizing liquid obtained in step (1) is applied to the surface of the outer and inner layers of the cardboard blank obtained in step (3), and dried to obtain the final product.

[0055] The waste protein raw material mentioned in step (1) is waste feathers; the hydrolysis is alkaline hydrolysis, and the hydrolysis conditions are: alkaline aqueous solution concentration 1.0 wt%, temperature 95℃, time 4 hours.

[0056] The hydrophobic modifier mentioned in step (1) is vinyltrimethoxysilane; the amount of hydrophobic modifier used is 15% of the dry protein mass.

[0057] Step (1) also includes a crosslinking modification step: a crosslinking agent is added to the modified protein solution, and the reaction is carried out at 60°C and pH 10 for 3 hours to obtain a crosslinked-modified protein solution; the crosslinking agent is epichlorohydrin, and the amount used is 8% of the dry weight of the protein.

[0058] The biomass adhesive in step (2) has a solid content of 25% and a viscosity of 5000 mPa·s; the gelatinization temperature is 50℃.

[0059] The negative pressure of the negative pressure drying in step (3) is -0.06 MPa, the drying temperature is 90℃, and the drying time is 5 minutes.

[0060] The coating amount mentioned in step (4) is 8 g / m 2 The drying temperature is 100℃.

[0061] The basis weight of the facial tissue is 200 g / m³. 2 The basis weight of the inner paper is 150 g / m². 2 The basis weight of the first corrugated base paper is 150 g / m². 2 The basis weight of the second corrugated base paper is 120 g / m². 2 The quantitative amount of the intermediate flat layer is 100 g / m. 2 .

[0062] Comparative Example 1 Based on Example 1, the intermediate flat layer is omitted, and the rest remains the same as in Example 1.

[0063] Comparative Example 2 Based on Example 1, the A-flute corrugated cardboard is omitted, and the rest remains the same as in Example 1.

[0064] Comparative Example 3 Based on Example 1, the surface sizing agent was replaced with an acrylic waterproof coating, and the coating amount was 6 g / m². 2 The rest remains the same as in Example 1.

[0065] Comparative Example 4 Based on Example 1, the surface sizing agent was replaced with waste protein hydrolysate that was not modified with silane and was not cross-linked, while the rest remained the same as in Example 1.

[0066] Comparative Example 5 Based on Example 1, the interlayer adhesive was replaced with a starch adhesive that is free of plant protein and nano-montmorillonite, while the rest remained the same as in Example 1.

[0067] Comparative Example 6 Based on Example 1, the composite drying process was changed to atmospheric pressure hot air drying (temperature 120℃, time 3min), while the rest remained the same as in Example 1.

[0068] Performance testing Strength: According to GB / T 6546 standard, the sample of the example and comparative example was cut into 25mm×100mm specimens and the edge crush strength was tested by compression tester at a speed of 12.5 mm / min. Moisture resistance: According to GB / T 1540-2002 standard, 100 cm 2 A circular sample is clamped on the Cobb absorber, 100 mL of distilled water is poured in, and after contact for 30 min, excess water is removed and the sample is weighed to determine the increase in mass. The surface contact angle is tested according to GB / T 30693 standard; After placing the sample in an environment with a temperature of 25℃ and a relative humidity of 90% for 24 hours, test the edge crush strength and calculate the retention rate = (strength after high humidity / initial strength) × 100%.

[0069] The data results show that this invention significantly improves the overall performance of paperboard through synergistic innovation in "structure-materials-process": the edge crush strength of the embodiment reaches 7.3-7.8 kN / m, and the Cobb value does not exceed 20 g / m. 2 The contact angle is 102-110°, and the high-humidity strength retention rate is ≥85%. Comparative Example 1 lacks an intermediate flat pressure layer; the stress transfer between the A and B flutes is interrupted, failing to form an overall "I-beam" effect. The flutes are prone to instability and buckling, resulting in a significant decrease in strength. Comparative Example 2 lacks an A flute, significantly reducing its load-bearing capacity. Comparative Example 3 uses an acrylic sizing agent that only forms a surface film, without reinforcing the inter-fiber bond, resulting in slightly lower strength and significantly reduced moisture resistance. Comparative Example 4, without hydrophobic modification, has strong hydrophilicity, failing to form an effective moisture barrier and exhibiting severe moisture absorption. Although it has some film-forming properties, the film is not water-resistant, softening under high humidity and significantly reducing strength. Comparative Example 5 uses traditional starch adhesive with insufficient bonding strength and lacks the water-resistant reinforcement of nano-montmorillonite, resulting in weak interlayer bonding. Under high humidity, the starch adhesive softens, causing interlayer slippage and significant strength loss. Comparative Example 6, high-temperature drying leads to fiber embrittlement and strength loss; the surface sizing film may also be damaged. Overall performance is lower than Example 1, indicating that negative pressure low-temperature drying protects fiber strength and improves product quality.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A moisture-proof, high-strength corrugated cardboard, characterized in that, It is composed of a surface layer, a first corrugated layer, an intermediate flat pressing layer, a second corrugated layer, and an inner layer in sequence; The first corrugated layer is type A corrugated, with a corrugation height of 4.5-5.5 mm; The second corrugated layer is a type B corrugated layer with a corrugation height of 2.5-3.2 mm; Both the surface of the top layer and the inner layer are coated with a waste protein-based modified sizing agent layer.

2. The moisture-proof high-strength corrugated cardboard according to claim 1, characterized in that, The surface layer and the first corrugated layer, the first corrugated layer and the intermediate flat layer, the intermediate flat layer and the second corrugated layer, and the second corrugated layer and the inner layer are bonded together by biomass adhesive. The biomass adhesive comprises the following components in parts by weight: 100 parts starch, 20-30 parts plant protein, 3-8 parts nano-montmorillonite, and 1-2 parts borax.

3. A method for preparing moisture-proof high-strength corrugated cardboard as described in claim 1, characterized in that, Includes the following steps: (1) Preparation of waste protein-based modified sizing agent: Hydrolyze waste protein raw materials to obtain protein hydrolysate; add hydrophobic modifier to protein hydrolysate and react to obtain modified protein solution; The modified protein solution is mixed with the adhesive to prepare a surface sizing solution; (2) Preparation of biomass adhesive: Mix starch, plant protein, nano-montmorillonite, borax and water, and gelatinize at 40-55℃ to obtain biomass adhesive; (3) Lamination: The face paper, the first corrugated base paper, the middle flat-pressed base paper, the second corrugated base paper, and the liner paper are laminated on a laminating machine using the biomass adhesive obtained in step (2), and dried under negative pressure to obtain a paperboard blank; (4) Surface sizing: The surface sizing liquid obtained in step (1) is applied to the surface of the outer and inner layers of the cardboard blank obtained in step (3), and dried to obtain the final product.

4. The method for preparing moisture-proof high-strength corrugated cardboard according to claim 3, characterized in that, The waste protein raw material mentioned in step (1) is at least one of waste feathers and leather scraps; the hydrolysis is alkaline hydrolysis, and the hydrolysis conditions are: alkaline aqueous solution concentration 0.1-1.0 wt%, temperature 70-95℃, time 2-4 hours.

5. The method for preparing moisture-proof high-strength corrugated cardboard according to claim 3, characterized in that, The hydrophobic modifier mentioned in step (1) is at least one of vinyltrimethoxysilane and vinyltriethoxysilane; the amount of hydrophobic modifier used is 5-15% of the dry weight of the protein.

6. The method for preparing moisture-proof high-strength corrugated cardboard according to claim 3, characterized in that, Step (1) also includes a crosslinking modification step: adding a crosslinking agent to the modified protein solution and reacting it at 40-60℃ and pH 8-10 for 1-3 hours to obtain a crosslinked-modified protein solution; the crosslinking agent is epichlorohydrin, and the amount used is 3-8% of the dry weight of the protein.

7. The method for preparing moisture-proof high-strength corrugated cardboard according to claim 3, characterized in that, The biomass adhesive in step (2) has a solid content of 20-25% and a viscosity of 3000-5000 mPa·s; the gelatinization temperature is 45-50℃.

8. The method for preparing moisture-proof high-strength corrugated cardboard according to claim 3, characterized in that, The negative pressure of the negative pressure drying in step (3) is -0.03 to -0.06 MPa, the drying temperature is 70-90℃, and the drying time is 3-5 minutes.

9. The method for preparing moisture-proof high-strength corrugated cardboard according to claim 3, characterized in that, The coating amount mentioned in step (4) is 5-8 g / m². 2 The drying temperature is 80-100℃.

10. The moisture-proof high-strength corrugated cardboard according to claim 1, characterized in that, The basis weight of the facial tissue is 150-200 g / m³. 2 The basis weight of the inner paper is 120-150 g / m². 2 The basis weight of the first corrugated base paper is 120-150 g / m². 2 The basis weight of the second corrugated base paper is 100-120 g / m². 2 The quantitative density of the intermediate flat layer is 80-100 g / m³. 2 .

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