Waterproof flame-retardant composite corrugated paperboard and preparation process thereof

Abstract

This invention discloses a waterproof and flame-retardant composite corrugated cardboard and its preparation process, comprising, in sequence, a face paper layer, a reinforcing composite layer, an adhesive layer, an upper core paper layer, a cushioning composite layer, a lower core paper layer, an adhesive layer, a reinforcing composite layer, and an inner paper layer. The cushioning composite layer is made of flame-retardant modified polyurethane foam. The upper and lower core paper layers are bonded to the upper and lower adhesive layers using flame-retardant modified polyurethane adhesives. The beneficial effects of this invention are: by using polyurethane foam as the cushioning composite layer and employing special polyurethane adhesives, the corrugated cardboard exhibits excellent waterproof properties. This material effectively prevents moisture penetration, thereby improving the service life and stability of the cardboard in humid environments; through the synergistic effect of the adhesives and the flame-retardant components of the polyurethane foam, the flame-retardant and fire-resistant capabilities of the cardboard box of this invention are greatly enhanced.

Description

Technical Field

[0001] This invention relates to the technical field of corrugated cardboard preparation, specifically to a waterproof and flame-retardant composite corrugated cardboard and its preparation process. Background Technology

[0002] Corrugated cardboard is a multi-layered adhesive, consisting of at least one layer of corrugated core paper and one layer of cardboard. It possesses high mechanical strength, capable of withstanding impacts and drops during handling. The actual performance of corrugated cardboard depends on three factors: the characteristics of the core paper and cardboard, and the structure of the carton itself. Corrugated cardboard offers three main advantages as a packaging material: 1) Low production cost: the resulting packaging containers are lightweight, foldable, and easy to store and transport. The cost of the raw paper is far lower than that of other materials such as plastics and metals; 2) Easy recycling: meeting green packaging requirements, corrugated cardboard can be recycled and used as raw material for pulp or molding production, or it can be used to produce corrugated cardboard again; 3) Easy processing: it can be processed into the packaging containers needed for goods through die-cutting, creasing, and folding, with simple and easy operation. The production process of corrugated cardboard has become highly automated and streamlined. Continuous production lines complete corrugating, gluing, laminating, drying, and shaping on the same machine, resulting in high production speed, low cost, and guaranteed quality.

[0003] Because the main component of corrugated cardboard is plant cellulose, it dehydrates and oxidizes as the temperature rises when heated. At room temperature, the oxygen index of corrugated cardboard is only 15%, classifying it as flammable. When the cardboard comes into contact with moisture, the fibers absorb water and swell, causing the cardboard to soften, deform, and even lose its original strength. This results in poor waterproof and flame-retardant properties. Typically, during transportation or storage, corrugated cardboard's overall strength is significantly reduced after encountering water, affecting its lifespan and making it inconvenient for use. In the warehousing and transportation processes of e-commerce, logistics, and express delivery industries, large quantities of corrugated cardboard boxes are piled up, posing a significant fire safety hazard. News reports frequently document fires caused by the flammability of piled-up corrugated cardboard boxes in factories, warehouses, transport vehicles, residential building corridors, and recycling stations, resulting in numerous personal and / or property losses. To address these issues, while strengthening fire safety awareness, it is necessary to modify corrugated cardboard to be waterproof and flame-retardant.

[0004] Existing methods for modifying corrugated cardboard to be waterproof and flame-retardant mainly involve adding flame retardants to the pulp, impregnating the finished product, or surface coating. These methods apply flame retardants to the interior or surface of the corrugated cardboard, inhibiting the generation of flammable gases by hindering the thermal decomposition of fibers, isolating heat and combustion-supporting gases, or diluting flammable gases. However, adding flame retardants to the pulp significantly affects the formability and processability of the corrugated cardboard, while impregnation methods affect its flatness, stiffness, and sizing properties. Surface coatings have poor durability; the coating may wear down over time or during use, gradually weakening its flame-retardant effect. Especially in high-friction or humid environments, the coating may peel off or be damaged, thus affecting the flame-retardant performance of the corrugated cardboard. Summary of the Invention

[0005] To address the above shortcomings, the present invention provides the following technical solution:

[0006] A waterproof and flame-retardant composite corrugated cardboard and its manufacturing process are disclosed, comprising a face paper layer, a reinforcing composite layer, an adhesive layer, an upper core paper layer, a cushioning composite layer, a lower core paper layer, an adhesive layer, a reinforcing composite layer, and an inner paper layer arranged sequentially. The cushioning composite layer is made of flame-retardant modified polyurethane foam. The upper and lower core paper layers are bonded to the upper and lower adhesive layers using flame-retardant modified polyurethane adhesive. The cushioning composite layer has peak-shaped structures on both the top and bottom that fit the corrugated structures of the upper and lower core paper layers.

[0007] The polyurethane adhesive includes component A, comprising...

[0008] Isocyanates: 5-10 parts of diphenylmethane diisocyanate (MDI) and 5-10 parts of toluene diisocyanate (TDI);

[0009] Flame retardant: 5-10 parts triphenyl phosphate, 10-15 parts diphenyl methyl phosphate, 4-5 parts dimethyl phosphonate, 1-3 parts melamine, 3-5 parts melamine phosphate;

[0010] Catalyst: 0.3–0.5 parts of organotin catalyst;

[0011] Plasticizer: 3-5 parts of tricaprylic acid glyceride

[0012] Antioxidant: 0.5-1 part of 2,6-di-tert-butyl-p-cresol (BHT);

[0013] Filler: 5-8 parts of nano-titanium dioxide powder;

[0014] Solvent: 10-30 parts acetone;

[0015] Component B includes:

[0016] 20-40 parts of polytetrahydrofuran (PTMG), 2-4 parts of polyethylene glycol (PEG), 1-3 parts of polybutane glycol, 0.2-1 part of 1,4-butanediol, 0.4-1 part of diethylene glycol, 0.1-0.5 parts of sodium benzoate, 0.2-0.6 parts of silane coupling agent 3-aminopropyltriethoxysilane, and 3-5 parts of bentonite filler;

[0017] The polyurethane foam comprises the following components in parts by weight.

[0018] Toluene diisocyanate (TDI) 40-50 parts, polytetrahydrofuran (PTMG) 30-40 parts, polybutanediol 10-20 parts, foaming agent water 1-5 parts, organotin catalyst 0.1-0.5 parts, epoxidized soybean oil 1-5 parts, aluminum hydroxide 10-20 parts, magnesium hydroxide 5-10 parts, calcium titanate 2-5 parts, antimony trioxide 2-5 parts, expanded graphite 5-10 parts.

[0019] Furthermore, the reinforcing composite layer is a reinforcing layer made of non-woven fabric or glass fiber mesh, and the upper and lower layers are bonded together by the polyurethane adhesive.

[0020] Furthermore, the particle size range of the nano-titanium dioxide powder used in the polyurethane adhesive is 20–50 nm.

[0021] Furthermore, the organotin catalyst is dibutyltin (DBT).

[0022] Furthermore, the ratio of component A to component B in the polyurethane adhesive is 1.5:1.

[0023] Furthermore, the face paper layer, adhesive layer, and inner paper layer are all made of kraft paper.

[0024] Furthermore, the upper and lower peak-shaped structures of the buffer composite layer are bonded together with the corrugations of the upper and lower core paper layers using adhesive to form a wave-shaped adhesive layer.

[0025] A manufacturing process for a waterproof and flame-retardant composite corrugated cardboard includes the following steps:

[0026] S1. Material Preparation

[0027] Prepare the corresponding chemical reagents, fiberglass mesh, non-woven fabric, kraft paper, and single-sided corrugated cardboard according to the above formula.

[0028] S2. Buffer Layer Preparation

[0029] Polyurethane foam is prepared according to the polyurethane foam formula, and then cut into sheet-like structures with corrugated cardboard on both sides according to the corrugated cardboard structure and size.

[0030] S3. Polyurethane adhesive preparation

[0031] Accurately weigh all liquid chemicals in component A, add acetone as solvent and stir until homogeneous, ensuring that the isocyanate is completely dissolved in the solution; then add nano titanium dioxide powder and antioxidant BHT to the mixture, mix thoroughly and ensure uniform dispersion;

[0032] Weigh out the corresponding mass fractions of component B, and mix polytetrahydrofuran (PTMG), polyethylene glycol (PEG), polybutane glycol, 1,4-butanediol, and diethylene glycol in the specified ratio. Add sodium benzoate, 3-aminopropyltriethoxysilane, and bentonite. Stir to ensure uniform dispersion. Then mix components A and B in a ratio of 1.5:1, stir evenly, and store for later use.

[0033] S4. Material Pretreatment

[0034] Cut the non-woven fabric to the corresponding size according to the corrugated cardboard;

[0035] S5. Material Composite

[0036] Polyurethane adhesive is coated on the flute of single-sided corrugated cardboard, corresponding to the flute of the foam sheet, and then laminated, flattened, and dried with hot air at 40-60℃ for 1-2 hours; the process is repeated on the other side of the foam sheet so that the buffer layer prepared by polyurethane foam is laminated with single-sided corrugated cardboard structure on both sides; and dried with hot air at 40-60℃ for 1-2 hours.

[0037] S6. Reinforcing layer composite

[0038] Coat one side of the cardboard structure obtained in the previous step with polyurethane adhesive, laminate with a layer of non-woven fabric, flatten, and dry with hot air at 40-60℃ for 1-2 hours; then coat the non-woven fabric with polyurethane adhesive, laminate with a layer of kraft paper, flatten, and dry with hot air at 40-60℃ for 1-2 hours.

[0039] S7. Reprocessing

[0040] The obtained cardboard is cut, trimmed, and cut into the shape of the corresponding product; a waterproof coating is sprayed on the surface of the cardboard, and dried with hot air at 40-60℃. The waterproof coating of this invention is an epoxy resin waterproof coating with a coating thickness of 0.3mm-0.5mm.

[0041] S8. Detection

[0042] The product's strength, waterproofing, and flame retardancy were tested accordingly.

[0043] S9 storage in standby

[0044] Store the resulting corrugated cardboard in a warehouse with a suitable environment.

[0045] The beneficial effects of this invention are: 1. This invention uses polyurethane foam as a cushioning composite layer and a special polyurethane adhesive, giving the corrugated cardboard excellent water resistance. This material effectively prevents moisture penetration, thereby improving the service life and stability of the cardboard in humid environments; 2. Through the synergistic effect of the adhesive and the flame-retardant components of the polyurethane foam, the flame-retardant and fire-resistant capabilities of the cardboard box of this invention are greatly enhanced; 3. Although this invention enhances strength and durability, this composite corrugated cardboard still maintains a relatively light weight. Furthermore, the materials used, such as polyurethane foam and natural paper materials, meet environmental protection requirements, are recyclable, and reduce environmental impact; 4. The cardboard of this invention has corresponding adjustability. By changing the materials, thickness, and structure of each component layer, the performance of the corrugated cardboard can be customized according to different application needs. For example, waterproof, flame-retardant, and compression-resistant properties can be adjusted to meet specific usage requirements. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the cross-sectional structure of the present invention;

[0047] In the diagram: 1-face paper layer, 2-reinforcing composite layer, 3-adhesive layer, 4-upper core paper layer, 5-buffer layer, 6-lower core paper layer, 7-inner paper layer. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Combination Figure 1 Shown:

[0050] A waterproof and flame-retardant composite corrugated cardboard includes, in sequence, a face paper layer, a reinforcing composite layer, an adhesive layer, an upper core paper layer, a cushioning composite layer, a lower core paper layer, an adhesive layer, a reinforcing composite layer, and an inner paper layer. The cushioning composite layer is made of flame-retardant modified polyurethane foam. The upper and lower core paper layers are bonded together with flame-retardant modified polyurethane adhesive. The reinforcing composite layer is a non-woven fabric composite reinforcing layer, which is bonded to the upper and lower layers with polyurethane adhesive. The upper and lower sides of the cushioning composite layer are both peak-shaped structures that conform to the corrugation of the core paper. The upper and lower peak-shaped structures of the cushioning composite layer are bonded together with the corrugations of the upper and lower core paper layers with adhesive to form a corrugated adhesive layer.

[0051] In this embodiment of the invention, the particle size range of the nano-titanium dioxide powder is 20-50 nm; the organic tin catalyst is dibutyltin (DBT); and the ratio of component A to component B is 1.5:1.

[0052] The polyurethane adhesive of the present invention includes

[0053] Component A isocyanates: 5-10 parts of diphenylmethane diisocyanate (MDI) and 5-10 parts of toluene diisocyanate (TDI).

[0054] Flame retardant: 5-10 parts triphenyl phosphate, 10-15 parts diphenyl methyl phosphate, 4-5 parts dimethyl phosphonate, 1-3 parts melamine, 3-5 parts melamine phosphate.

[0055] Catalyst: 0.3-0.5 parts of organotin catalyst,

[0056] Plasticizer: 3-5 parts of tricaprylic acid glyceride

[0057] Antioxidant: 0.5-1 part of 2,6-di-tert-butyl-p-cresol (BHT)

[0058] Filler: 5-8 parts of nano-titanium dioxide powder

[0059] Solvent: 10-30 parts acetone;

[0060] Component B includes:

[0061] 20-40 parts of polytetrahydrofuran (PTMG), 2-4 parts of polyethylene glycol (PEG), 1-3 parts of polybutane glycol, 0.2-1 part of 1,4-butanediol, 0.4-1 part of diethylene glycol, 0.1-0.5 parts of sodium benzoate, 0.2-0.6 parts of silane coupling agent 3-aminopropyltriethoxysilane, and 3-5 parts of bentonite filler;

[0062] Polyurethane foam comprises the following components in parts by weight.

[0063] Toluene diisocyanate (TDI) 40-50 parts, polytetrahydrofuran (PTMG) 30-40 parts, polybutanediol 10-20 parts, foaming agent water 1-5 parts, organotin catalyst 0.1-0.5 parts, epoxidized soybean oil 1-5 parts, aluminum hydroxide 10-20 parts, magnesium hydroxide 5-10 parts, calcium titanate 2-5 parts, antimony trioxide 2-5 parts, expanded graphite 5-10 parts.

[0064] A waterproof and flame-retardant composite corrugated cardboard, the preparation process of which is as follows:

[0065] Example

[0066] S1. Material preparation: Prepare the corresponding chemical reagents according to the above formula. All the reagents used in this invention are standard reagents that are routinely purchased from the market.

[0067] Fiberglass mesh (mesh size 10mm×10mm, 120g / m) 2 Up to 200g / m 2 Non-woven fabrics (60-120 g / m², polypropylene non-woven fabric, PP non-woven fabric) and kraft paper (40 g / m² to 200 g / m²), single-sided corrugated cardboard (A, B, C flutes);

[0068] S2. Buffer Layer Preparation

[0069] Polyurethane foam is prepared according to the polyurethane foam formula, and then cut into sheet-like structures with corrugations on both sides according to the flute structure and size of two single-sided corrugated cardboard.

[0070] Polyurethane foam comprises the following components H1 in parts by weight

[0071] 40 parts of toluene diisocyanate (TDI), 30 parts of polytetrahydrofuran (PTMG), 10 parts of polybutanediol, 1 part of foaming agent water, 0.1 part of organotin catalyst, 1 part of epoxidized soybean oil, 10 parts of aluminum hydroxide, 5 parts of magnesium hydroxide, 2 parts of calcium titanate, 2 parts of antimony trioxide, and 5 parts of expanded graphite.

[0072] Polyurethane foam comprises the following components in parts by weight: H2

[0073] 50 parts of toluene diisocyanate (TDI), 40 parts of polytetrahydrofuran (PTMG), 20 parts of polybutanediol, 5 parts of foaming agent water, 0.5 parts of organotin catalyst, 5 parts of epoxidized soybean oil, 20 parts of aluminum hydroxide, 10 parts of magnesium hydroxide, 5 parts of calcium titanate, 5 parts of antimony trioxide, and 10 parts of expanded graphite.

[0074] S3. Polyurethane adhesive preparation

[0075] Accurately weigh all liquid chemicals in component A, add acetone as solvent and stir until homogeneous, ensuring that the isocyanate is completely dissolved in the solution; then add nano titanium dioxide powder and antioxidant BHT to the mixture, mix thoroughly and ensure uniform dispersion;

[0076] Weigh out the corresponding mass parts of component B, and mix 20-40 parts of polytetrahydrofuran (PTMG), polyethylene glycol (PEG), polybutanediol, 1,4-butanediol, and diethylene glycol in the specified ratio. Add sodium benzoate, 3-aminopropyltriethoxysilane, and 3-5 parts of bentonite. Stir until uniformly dispersed.

[0077] Polyurethane adhesive component A1

[0078] Isocyanates: 5 parts diphenylmethane diisocyanate (MDI), 5 parts toluene diisocyanate (TDI),

[0079] Flame retardant: 5 parts triphenyl phosphate, 10 parts diphenyl methyl phosphate, 4 parts dimethyl phosphonate, 1 part melamine, 3 parts melamine phosphate.

[0080] Catalyst: 0.3 parts of organotin catalyst dibutyltin (DBT).

[0081] Plasticizer: 3 parts glyceryl triethyl acetate,

[0082] Antioxidant: 0.5 parts of 2,6-di-tert-butyl-p-cresol (BHT)

[0083] Filler: 5 parts nano-titanium dioxide powder

[0084] Solvent: 10-30 parts acetone, add according to actual conditions;

[0085] Component B1 includes:

[0086] 20 parts polytetrahydrofuran (PTMG), 2 parts polyethylene glycol (PEG), 1 part polybutanediol, 0.2 parts 1,4-butanediol, 0.4 parts diethylene glycol, 0.1 parts sodium benzoate, 0.2 parts silane coupling agent 3-aminopropyltriethoxysilane, and 3 parts bentonite filler;

[0087] Component A2 isocyanates: 10 parts diphenylmethane diisocyanate (MDI) and 10 parts toluene diisocyanate (TDI).

[0088] Flame retardant: 10 parts triphenyl phosphate, 15 parts diphenyl methyl phosphate, 5 parts dimethyl phosphonate, 3 parts melamine, 5 parts melamine phosphate.

[0089] Catalyst: 0.5 parts organotin catalyst,

[0090] Plasticizer: 5 parts of tricaprylic acid glyceride

[0091] Antioxidant: 1 part of 2,6-di-tert-butyl-p-cresol (BHT)

[0092] Filler: 8 parts nano-titanium dioxide powder

[0093] Solvent: 10-30 parts acetone, add according to actual conditions;

[0094] Component B2 includes:

[0095] 40 parts of polytetrahydrofuran (PTMG), 4 parts of polyethylene glycol (PEG), 3 parts of polybutanediol, 1 part of 1,4-butanediol, 1 part of diethylene glycol, 0.5 parts of sodium benzoate, 0.6 parts of silane coupling agent 3-aminopropyltriethoxysilane, and 5 parts of filler bentonite.

[0096] Mix components A1 and B1, as well as components A2 and B2, in a ratio of 1.5:1, stir well, and store for later use.

[0097] S4. Material Pretreatment

[0098] Cut the non-woven fabric to the corresponding size according to the dimensions of the single-sided corrugated cardboard;

[0099] S5. Material Composite

[0100] Polyurethane adhesive is coated on the flute of single-sided corrugated cardboard, corresponding to the flute of the foam sheet, and then laminated, flattened, and dried with hot air at 40-60℃ for 1-2 hours; the process is repeated on the other side of the foam sheet so that the buffer layer prepared by polyurethane foam is laminated with single-sided corrugated cardboard structure on both sides; and dried with hot air at 40-60℃ for 1-2 hours.

[0101] S6. Reinforcing layer composite

[0102] Coat one side of the cardboard structure obtained in the previous step with polyurethane adhesive, laminate a layer of non-woven fabric (or fiberglass mesh), then coat the non-woven fabric with polyurethane adhesive, laminate a layer of kraft paper on top, flatten it, and dry it with hot air at 40-60℃ for 1-2 hours.

[0103] S7. Reprocessing

[0104] The obtained cardboard is cut, trimmed, and shaped into the corresponding product. A waterproof coating is then sprayed onto the surface of the cardboard, and it is dried with hot air at 40-60℃. The waterproof coating of this invention is an epoxy resin waterproof coating with a coating thickness of 0.3mm-0.5mm. Depending on the actual situation, those skilled in the art can choose other coatings with waterproof and flame-retardant effects. If necessary, an appropriate amount of nano-silica can be added to the coating to increase its waterproof and fireproof performance.

[0105] S8. Detection

[0106] The strength, waterproof and flame retardant properties of the products are tested. The strength, waterproof and flame retardant properties are tested manually or with corresponding equipment, and qualified quality corrugated cardboard is selected by batch.

[0107] S9 storage in standby

[0108] Store the obtained corrugated cardboard in a warehouse with a suitable environment, ensuring appropriate humidity and temperature.

[0109] The following embodiments of the present invention use two U-shaped A-flute single-face corrugated cardboard pieces; fiberglass mesh (mesh size 10mm×10mm, 120g), which can be adjusted according to actual needs in specific implementations; non-woven fabric (60 g / m², polypropylene non-woven fabric, PP non-woven fabric) and kraft paper (60 g / m²). In the embodiments of the present invention, the face paper layer, adhesive layer, and inner paper layer are all made of kraft paper of the same specification, which can be adjusted according to actual needs in specific implementations; the single-face corrugated cardboard is U-shaped (A-flute), and the specific flute shape of the upper and lower core layers can be adjusted according to actual needs;

[0110] Example 1

[0111] Adhesive: A1B1

[0112] Polyurethane foam: H1

[0113] Reinforcing composite layer: Non-woven fabric, 60 g / m², polypropylene non-woven fabric (PP non-woven fabric)

[0114] Example 2

[0115] Adhesive: A2B2

[0116] Polyurethane foam: H2

[0117] Reinforcing composite layer: Non-woven fabric, 60 g / m², polypropylene non-woven fabric (PP non-woven fabric)

[0118] Example 3

[0119] Adhesive: A1B1

[0120] Polyurethane foam: H2

[0121] Reinforcing composite layer: Non-woven fabric, 60 g / m², polypropylene non-woven fabric (PP non-woven fabric)

[0122] Example 4

[0123] Adhesive: A2B2

[0124] Polyurethane foam: H1

[0125] Reinforcing composite layer: Non-woven fabric, 60 g / m², polypropylene non-woven fabric (PP non-woven fabric)

[0126] Example 5

[0127] Adhesive: A1B1

[0128] Polyurethane foam: H1

[0129] Reinforcing composite layer: Fiberglass mesh, 10mm×10mm mesh size, 120g / m² 2

[0130] Testing revealed that the corrugated cardboard obtained in the above embodiments all possessed high compressive strength, more than three times that of conventional corrugated cardboard. Water droplets could not penetrate the cardboard. Compared to existing corrugated cardboard, in standard flame exposure tests, the modified corrugated cardboard of this invention only showed slight blackening on the surface within 10 seconds of flame exposure, without significant carbonization or damage. After 30 seconds of flame exposure, the surface of the cardboard began to slightly carbonize, but the flame did not spread to the interior of the cardboard, nor did it cause deep damage. After 1 minute of flame exposure, the surface of the cardboard was significantly carbonized, but the flame did not spread further, maintaining good fire resistance. Compared to traditional corrugated cardboard, the modified corrugated cardboard exhibited significantly improved fire resistance under flame exposure, indicating better fire-resistant properties and safety.

[0131] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0132] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A waterproof and flame-retardant composite corrugated cardboard, characterized in that: The assembly includes, in sequence, a face paper layer, a reinforcing composite layer, an adhesive layer, an upper core paper layer, a cushioning composite layer, a lower core paper layer, an adhesive layer, a reinforcing composite layer, and an inner paper layer. The cushioning composite layer is made of flame-retardant modified polyurethane foam. The upper and lower core paper layers are bonded together with flame-retardant modified polyurethane adhesives. The cushioning composite layer has peak-shaped structures on both the top and bottom that fit into the corrugated structures of the upper and lower core paper layers. The polyurethane adhesive includes Component A includes: Isocyanates: 5-10 parts of diphenylmethane diisocyanate (MDI) and 5-10 parts of toluene diisocyanate (TDI); Flame retardant: 5-10 parts triphenyl phosphate, 10-15 parts diphenyl methyl phosphate, 4-5 parts dimethyl phosphonate, 1-3 parts melamine, 3-5 parts melamine phosphate; Catalyst: 0.3–0.5 parts of organotin catalyst; Plasticizer: 3-5 parts of trioctyl oleate; Antioxidant: 0.5-1 part of 2,6-di-tert-butyl-p-cresol (BHT); Filler: 5-8 parts of nano-titanium dioxide powder; Solvent: 10-30 parts acetone; Component B includes: 20-40 parts of polytetrahydrofuran (PTMG), 2-4 parts of polyethylene glycol (PEG), 1-3 parts of polybutane glycol, 0.2-1 part of 1,4-butanediol, 0.4-1 part of diethylene glycol, 0.1-0.5 parts of sodium benzoate, 0.2-0.6 parts of silane coupling agent 3-aminopropyltriethoxysilane, and 3-5 parts of bentonite filler; The polyurethane foam comprises the following components in parts by weight. Toluene diisocyanate (TDI) 40-50 parts, polytetrahydrofuran (PTMG) 30-40 parts, polybutanediol 10-20 parts, foaming agent water 1-5 parts, organotin catalyst 0.1-0.5 parts, epoxidized soybean oil 1-5 parts, aluminum hydroxide 10-20 parts, magnesium hydroxide 5-10 parts, calcium titanate 2-5 parts, antimony trioxide 2-5 parts, expanded graphite 5-10 parts.

2. A waterproof and flame retardant composite corrugated paperboard according to claim 1, characterized in that: The reinforcing composite layer is a reinforcing layer made of non-woven fabric or glass fiber mesh, and the upper and lower layers are bonded together by the polyurethane adhesive.

3. A water-proof fire-retardant type composite corrugated paperboard according to claim 1, characterized in that: The particle size range of the nano-titanium dioxide powder used in the polyurethane adhesive is 20–50 nm.

4. A water-proof fire-retardant type composite corrugated paperboard according to claim 1, characterized in that: All organotin catalysts are dibutyltin (DBT).

5. A water-proof fire-retardant type composite corrugated paperboard according to claim 1, characterized in that: The ratio of component A to component B in the polyurethane adhesive is 1.5:

1.

6. A water-proof fire-retardant type composite corrugated paperboard according to claim 1, characterized in that: The face paper layer, adhesive layer, and inner paper layer are all made of kraft paper.

7. A water-proof fire-retardant type composite corrugated paperboard according to claim 1, characterized in that: The upper and lower peak-shaped structures of the buffer composite layer are bonded together with the corrugated structures of the upper and lower core paper layers by adhesive.

8. The process for preparing a waterproof and flame-retardant composite corrugated paperboard according to claim 1, characterized in that The preparation steps include the following: S1. Material Preparation Prepare the corresponding chemical reagents, fiberglass mesh, non-woven fabric, kraft paper, and single-sided corrugated cardboard according to the above formula. S2. Buffer Layer Preparation Polyurethane foam is prepared according to the polyurethane foam formula, and then cut into sheet-like structures with corrugated cardboard on both sides according to the corrugated cardboard structure and size. S3. Polyurethane adhesive formulation Accurately weigh all liquid chemicals in component A, add acetone as solvent and stir until homogeneous, ensuring that the isocyanate is completely dissolved in the solution; then add nano titanium dioxide powder and antioxidant BHT to the mixture, mix thoroughly and ensure uniform dispersion; Weigh out the corresponding mass parts of component B, and mix 20-40 parts of polytetrahydrofuran (PTMG), 2-4 parts of polyethylene glycol (PEG), 1-3 parts of polybutanediol, 0.2-1 parts of 1,4-butanediol, and 0.4-1 parts of diethylene glycol according to the specified ratio. Add 0.1-0.5 parts of sodium benzoate, 0.2-0.6 parts of 3-aminopropyltriethoxysilane, and 3-5 parts of bentonite, ensuring uniform dispersion. Mix components A and B in a ratio of 1.5:1, stir well, and store for later use. S4. Material Pretreatment Cut the non-woven fabric to the corresponding size according to the corrugated cardboard; S5. Material Composite Polyurethane adhesive is coated on the flute of single-sided corrugated cardboard, corresponding to the flute of the foam sheet, and then laminated, flattened, and dried with hot air at 40-60℃ for 1-2 hours; the process is repeated on the other side of the foam sheet so that the buffer layer prepared by polyurethane foam is laminated with single-sided corrugated cardboard structure on both sides; and dried with hot air at 40-60℃ for 1-2 hours. S6. Reinforcing layer composite Coat one side of the cardboard structure obtained in the previous step with polyurethane adhesive, laminate with a layer of non-woven fabric, flatten, and dry with hot air at 40-60℃ for 1-2 hours; then coat the non-woven fabric with polyurethane adhesive, laminate with a layer of kraft paper, flatten, and dry with hot air at 40-60℃ for 1-2 hours. S7. Reprocessing The obtained cardboard is cut, trimmed, and cut into the shape of the corresponding product; a waterproof coating is sprayed on the surface of the cardboard; and it is dried with hot air at 40-60℃. S8. Detection The product's strength, waterproofing, and flame retardancy were tested accordingly. S9 storage in standby Store the resulting corrugated cardboard in a warehouse with a suitable environment.

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