A high water-resistant formaldehyde-free cabinet composite board and its preparation method

Abstract

This invention discloses a highly water-resistant formaldehyde-free kitchen cabinet composite board and its preparation method, belonging to the field of environmentally friendly artificial board preparation technology. The composite board includes a waterproof and wear-resistant surface layer, a reinforcing core layer, and a balancing back layer, bonded together using a self-made formaldehyde-free adhesive. The preparation steps include preparing the waterproof and wear-resistant surface layer, preparing the reinforcing core layer, preparing the formaldehyde-free adhesive, and forming and post-processing the composite board. This invention addresses the problems of poor water resistance and insufficient bonding strength in traditional formaldehyde-free composite boards by using adhesive composite modification, multi-layer functional integration of the surface layer, hydrophobic reinforcement of the core layer, and synergistic processes to achieve formaldehyde-free composite board with high water resistance, excellent mechanical properties, and dimensional stability, making it suitable for the humid and high-temperature environment of the kitchen.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly engineered wood products manufacturing technology, and in particular to a highly water-resistant, formaldehyde-free cabinet composite board and its preparation method. Background Technology

[0002] With increasing environmental awareness and growing health demands, formaldehyde-free and environmentally friendly furniture boards have become the mainstream trend in the industry. As a core piece of furniture in the kitchen, kitchen cabinets are constantly exposed to humid and high-temperature environments, thus placing stringent requirements on the water resistance, mechanical properties, and environmental friendliness of the boards used.

[0003] Currently, most formaldehyde-free kitchen cabinet composite boards on the market are made using formaldehyde-free adhesives such as plant protein glue (e.g., soybean glue) and starch glue. However, traditional plant protein adhesives have obvious defects: on the one hand, plant protein molecules contain a large number of hydrophilic groups, resulting in extremely poor water resistance of the adhesive. Composite boards made with them are prone to delamination and bubbling in humid environments, and the 24-hour water absorption expansion rate often exceeds 10%, which cannot meet the requirements for kitchen cabinet use. On the other hand, traditional plant protein adhesives have low bonding strength, resulting in insufficient mechanical properties of composite boards such as static bending strength and internal bond strength, which limits their application in load-bearing kitchen cabinet materials.

[0004] To improve the water resistance of formaldehyde-free adhesives, existing technologies mostly employ physical modification (such as thermal modification and ultrasonic modification) or chemical modification (such as acylation and esterification) to treat plant proteins. However, the improvement effect of a single modification method is limited. Meanwhile, some technologies improve bonding strength by adding formaldehyde-based crosslinking agents, but this leads to excessive formaldehyde emissions from the boards, contradicting the original intention of formaldehyde-free and environmentally friendly products. Furthermore, the layered structure design of existing composite boards is unreasonable, making it difficult to simultaneously achieve surface wear resistance and core moisture resistance, further limiting their application in the kitchen cabinet industry.

[0005] Therefore, developing a cabinet composite board based on a novel formaldehyde-free adhesive that combines high water resistance and excellent mechanical properties to solve the technical problems of poor water resistance and insufficient bonding strength of traditional formaldehyde-free composite boards has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a highly water-resistant formaldehyde-free cabinet composite board and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a high water-resistant, formaldehyde-free cabinet composite board, which comprises, from top to bottom, a waterproof and wear-resistant surface layer, a reinforcing core layer, and a balancing back layer, bonded together with a self-made formaldehyde-free adhesive. The waterproof and wear-resistant surface layer is a thickened melamine board, 0.1-0.8 mm thick, possessing wear resistance, waterproofing, and flame retardant properties. The reinforcing core layer is a mixture of poplar fiber and crop straw treated with a 5% sodium hydroxide solution, with an added alkyl ketone dimer waterproofing agent, 14.6-15.6 mm thick, providing excellent mechanical support and internal waterproofing. The balancing back layer is waterproof kraft paper, 0.1-0.3 mm thick, balancing board stress and preventing warping. The self-made formaldehyde-free adhesive uses soy protein isolate, chitosan, and oxidized starch as core raw materials, pre-crosslinked and modified with photosensitive groups, resulting in formaldehyde-free release and excellent bonding strength.

[0009] A method for preparing a highly water-resistant, formaldehyde-free cabinet composite board includes the following steps:

[0010] S1. Preparation of waterproof and wear-resistant surface layer:

[0011] Decorative base paper is activated by plasma, cross-linked with melamine and γ-polyglutamic acid under citric acid catalysis, and then 5-8% of nano-sized aluminum hydroxide flame retardant is added to prepare a formaldehyde-free impregnation resin with a solid content of 45-50%. The activated decorative base paper is impregnated in the resin, pre-dried with hot air at 85-95℃ for 1.5-2 minutes, impregnated again, dried at 110-120℃ for 6 minutes, and finely sanded. A layer of ethanol solution containing γ-methacryloyloxypropyltrimethoxysilane is rolled onto its surface, dried, and then coated with polyurethane acrylate resin doped with 1.0-2.0 wt% nano-silica. After curing, a thickened melamine board with a thickness of 0.1-0.8 mm is obtained.

[0012] Plasma activation of decorative base paper is a physicochemical modification process. Its mechanism is that high-energy electrons, ions and free radicals generated by plasma discharge bombard the surface of base paper fibers. On the one hand, it breaks some CC and CH bonds in the cellulose molecular chain, so that active functional groups such as hydroxyl (-OH) and carboxyl (-COOH) are generated on the surface. On the other hand, it increases the surface roughness, which not only enhances the interfacial bonding force between the subsequent impregnation resin and the fiber, but also provides channels for resin penetration.

[0013] Melamine, as the crosslinking host, contains three amino groups (-NH2) in its molecule. Under the dual action of γ-polyglutamic acid, it achieves formaldehyde-free self-crosslinking. Citric acid, as a catalyst, provides a weakly acidic environment through its carboxyl groups (-COOH). The numerous free carboxyl groups (-COOH) and amino groups (-NH2) on the γ-polyglutamic acid molecular chain can, on the one hand, combine with the amino groups (-NH2) and triazine rings of melamine through hydrogen bonds; on the other hand, under citric acid catalysis and heating conditions, its carboxyl groups can undergo amidation condensation reactions with the amino groups of melamine, forming a "melamine-polyglutamic acid" crosslinking network. This network replaces the traditional melamine-formaldehyde condensate in the construction of the crosslinking network, avoiding the dependence of traditional melamine resin on formaldehyde. The chemical reaction formula can be represented as follows:

[0014] ;

[0015] Nano-sized aluminum hydroxide, as a flame-retardant filler, not only reduces the combustion temperature and dilutes combustible gases through endothermic decomposition (2Al(OH)3→Al2O3+3H2O), but also fills the voids in the resin network, improves the resin's density and water resistance, and enhances the mechanical strength of the impregnated base paper.

[0016] The two impregnation and drying steps serve a progressive purpose: the first impregnation is followed by pre-drying at 85-95℃ for 1.5-2 minutes to remove free water from the resin, allowing it to initially penetrate into the gaps between the base paper fibers, while simultaneously initiating the initial cross-linking of melamine and γ-polyglutamic acid; the second impregnation replenishes the resin load, ensuring that the base paper fibers are fully coated with resin to meet the "thickness" requirement; drying at 110-120℃ for 6 minutes provides sufficient energy for the polycondensation reaction, promotes further densification of the cross-linked network, fixes the resin morphology in the base paper, and prevents resin loss during subsequent processing. This stage is a continuation of the previous polycondensation reaction, transforming the resin from a linear / low cross-linked state to a highly cross-linked three-dimensional network;

[0017] Fine sanding is a physical modification step. Its function is to remove excess incompletely cross-linked resin from the surface of the base paper, smooth the surface protrusions, make the board thickness uniform, and further roughen the surface to increase the contact area between the subsequent coating layer and the substrate, improve the interfacial adhesion, and lay the foundation for the formation of the surface wear-resistant layer. The silanol (-Si(OH)3) produced by silane hydrolysis undergoes a condensation reaction with the -OH on the surface of the impregnated resin to form a strong Si-OC covalent bond. The methacryloyloxy group at the other end of the silane reagent molecule contains a C=C double bond, which can participate in the free radical copolymerization reaction of the resin during UV curing to form a covalent bond connection.

[0018] Nano-silica, as an inorganic reinforcing filler, is uniformly dispersed in polyurethane acrylate resin. It can fill the voids in the resin network, improve surface hardness, wear resistance and scratch resistance. At the same time, its hydrophobicity can improve the water resistance of the board surface, forming a synergy with the water resistance of the underlying impregnating resin.

[0019] S2. Preparation of the reinforced core layer:

[0020] Poplar fiber is mixed with crushed straw, sprayed with 5% sodium hydroxide solution, alkali treated at 50℃ for 4 hours, washed until neutral, and then pressed and dehydrated; it is then uniformly mixed with alkyl ketene dimer waterproofing agent emulsion, laid into a blank, pre-pressed at 180℃ and 2.5MPa for 5 minutes, and sanded to a standard thickness of 14.6-15.6mm and a specified density to obtain an inner waterproof reinforced core layer;

[0021] The core function of mixing poplar fiber with crushed straw is to achieve complementary raw materials. Poplar fiber is tough and has a suitable fiber length, while straw fiber is widely available and inexpensive. The mixture can form an interwoven support structure, providing a basic mechanical skeleton for the core layer. At the same time, it expands the contact area for subsequent alkali treatment and waterproofing agent action. Spraying with a 5% sodium hydroxide solution and alkali treatment at 50℃ for 4 hours is a key step in fiber activation. The mechanism is a hydrolysis and removal reaction under alkaline conditions: sodium hydroxide reacts with the acetyl groups of hemicellulose in the fiber in an ester hydrolysis reaction.

[0022] R-OOCH3 + NaOH → R-COONa + CH3OH

[0023] R represents the hemicellulose molecular chain. Simultaneously, the ether bonds (-O-) in lignin are hydrolyzed, causing the hemicellulose and some lignin wrapped on the surface of cellulose to dissolve and remove, exposing the hydroxyl groups (-OH) on the cellulose molecular chain, thus enhancing the reactivity of the fiber. In addition, the alkaline solution will cause the cellulose fiber to swell, break the hydrogen bonds between molecules, and increase the internal porosity of the fiber, creating conditions for the penetration and bonding of the subsequent waterproofing agent. Washing to neutral is to remove residual sodium hydroxide and hydrolysis products, avoiding alkaline substances from affecting the reactivity of the subsequent waterproofing agent. Pressing and dehydration are to control the fiber moisture content, ensuring uniformity when mixing with the waterproofing agent, and avoiding excessive moisture leading to uneven density after laying and forming the fabric.

[0024] The hydroxyl groups (-OH) on the surface of cellulose act as nucleophiles, launching a nucleophilic attack on the carbonyl carbon atom of the lactone ring in the alkyl ketene dimer molecule. This breaks the CO covalent bond of the lactone ring, forming an unstable four-membered ring transition state. The transition state rapidly rearranges, completely opening the lactone ring. The oxygen atom in the transition state then combines with the hydrogen atom (-H) of the cellulose hydroxyl group, ultimately forming an ester bond (-OC(=O)-) between the alkyl ketene dimer and the cellulose molecular chain. This covalently grafts the alkyl ketene dimer onto the cellulose surface.

[0025] ;

[0026] R1 and R2 are long-chain alkyl groups of alkyl ketene dimers. The long-chain alkyl groups of the alkyl ketene dimers are oriented outward to form a hydrophobic layer that hinders water penetration. At the same time, the alkyl ketene dimer emulsion is uniformly dispersed on the fiber surface. The unreacted alkyl ketene dimer molecules will melt and spread during the hot pressing process, further filling the fiber gaps and enhancing the density of the core layer. The preform is made by uniformly spreading the fiber mixed with the waterproofing agent to form a loose preform that meets the thickness requirements, preparing for subsequent hot pressing densification.

[0027] High temperature triggers the complete esterification reaction between alkyl ketene dimers and cellulose hydroxyl groups, and also reforms and strengthens the hydrogen bonds between fibers, enhancing the cohesion of the core layer. High pressure compacts the loose preform, reduces the gaps between fibers, and makes the fibers tightly interwoven. At the same time, it promotes the uniform spread of alkyl ketene dimers on the fiber surface, ensuring the continuity and integrity of the hydrophobic layer, ultimately improving the density and mechanical strength of the core layer. Sanding removes protrusions and excess fibers from the surface of the core layer, allowing the core layer thickness to be precisely controlled at 14.6-15.6 mm. It also smooths the surface, providing good interfacial contact conditions for subsequent bonding with the surface and back layers, and avoiding the impact of surface unevenness on the bonding strength. The entire process, through the continuous action of fiber activation, waterproof grafting, and hot pressing, ultimately yields a reinforced core layer with both high mechanical properties and internal waterproofing, and without the release of formaldehyde or other harmful substances, meeting environmental protection requirements.

[0028] S3. Preparation of formaldehyde-free adhesive:

[0029] S301, 50-60 parts of soy protein isolate were prepared into a 15wt% aqueous solution, 10-15 parts of chitosan were prepared into a 5wt% acetic acid solution, 20-30 parts of oxidized starch were added to deionized water, and the mixture was gelatinized at 85℃ for 30 min to obtain starch paste. The mixture was then mixed, and the pH was adjusted to 8.5 with 10% NaOH solution. The mixture was reacted at 55℃ and 300-400 r / min for 2.5 h to obtain a pre-crosslinked product with a viscosity of 5000-8000 mPa·s.

[0030] Soy protein isolate is prepared as a 15wt% aqueous solution to break the hydrogen bonds between protein molecules, allowing the molecular chains to unfold and exposing the free amino groups (-NH2) in the amino acid residues, thus providing reaction sites for subsequent cross-linking. Chitosan dissolves in a 5wt% acetic acid solution because the amino groups (-NH2) in the chitosan molecules are protonated (-NH3) under acidic conditions. +The process of pretreatment reduces intermolecular forces, allowing the starch to disperse evenly and partially expose hydroxyl (-OH) and amino groups, thus enhancing compatibility with other components and enabling it to participate in cross-linking reactions. Oxidized starch is gelatinized at 85°C for 30 minutes, which destroys the crystalline structure of starch at high temperature, causing the starch molecular chains to depolymerize and swell fully, exposing the aldehyde groups encapsulated in the molecules, providing sufficient active sites for cross-linking reactions. All three pretreatments are in a dispersed state after treatment, avoiding uneven local reactions.

[0031] Adjusting the pH to 8.5 with 10% NaOH solution after mixing is a key condition for the Schiff base reaction: the Schiff base reaction needs to be carried out in a weakly alkaline environment. This pH value can prevent the protonation of amino groups under acidic conditions and prevent the hydrolysis of protein molecular chains or the degradation of starch aldehyde groups under strong alkaline conditions. At the same time, it can activate the reactivity of amino and aldehyde groups, creating thermodynamic conditions for covalent cross-linking. Heating to 55℃ and stirring at 300-400 r / min provides the activation energy required for the reaction, accelerates molecular diffusion, and ensures full contact between amino and aldehyde groups. On the other hand, stirring breaks up the local gel agglomerates formed during the reaction, ensuring a uniform and dense cross-linked network.

[0032] The free amino groups on the soy protein isolate molecular chain act as nucleophiles, attacking the electron-deficient carbonyl carbon of the aldehyde group in oxidized starch molecules, undergoing a nucleophilic addition reaction to form an unstable imine intermediate. This intermediate then rapidly undergoes dehydration condensation to form a stable imine bond. Simultaneously, the amino groups in chitosan molecules can also undergo the same Schiff base reaction with the aldehyde groups of oxidized starch. Furthermore, hydrogen bonds are formed between the hydroxyl and amino groups of chitosan and soy protein isolate to assist cross-linking. Ultimately, through the covalent linkage of imine bonds and the synergistic effect of hydrogen bonds, a three-dimensional pre-crosslinked network is constructed. R represents a molecular chain segment in the above molecules.

[0033] ;

[0034] The synergistic effect of each component determines the high viscosity of the pre-crosslinked product: soy protein isolate provides a flexible framework for the network, the rigid segments of chitosan enhance the network strength, and oxidized starch acts as a crosslinking bridging agent to connect the two. The three-dimensional network formed by the Schiff base reaction restricts the movement of molecular chains, reducing the fluidity of the system and ultimately forming a pre-crosslinked product with a viscosity of 5000-8000 mPa·s. In addition, the aldehyde groups are covalently bonded to the inside of the network during the reaction, with no free formaldehyde released, which meets the requirements of formaldehyde-free environmental protection.

[0035] S302. Cool the pre-crosslinked product to 40℃, adjust the pH to 7.5 with 5% acetic acid solution, replace with nitrogen twice, add 5-10% glycidyl methacrylate by mass of the total system in three portions, react at 60℃ for 3 hours, add 2% activated carbon for adsorption for 30 minutes, vacuum filter, add 2-5% photoinitiator and 3-8% hydrophobic nano silica under light-protected environment, ultrasonically disperse for 20 minutes, then add 1-3% tannic acid, adjust the solid content to 30%, control the viscosity to 1500-2500 mPa·s, and obtain formaldehyde-free adhesive.

[0036] Cooling the pre-crosslinked product to 40°C and adjusting the pH to 7.5 with 5% acetic acid solution creates a suitable environment for the subsequent photosensitive grafting reaction. The weakly alkaline conditions can both prevent the hydrolysis of imine bonds in the pre-crosslinked network and activate the reactivity of epoxy groups, providing a thermodynamic advantage for the epoxy ring-opening reaction of glycidyl methacrylate (GMA). The core function of the two nitrogen purgings is to remove oxygen from the system, prevent oxygen from inhibiting the epoxy ring-opening reaction or oxidizing the amino groups in the pre-crosslinked network, and ensure the efficient progress of the grafting reaction.

[0037] Adding 5-10% GMA by three stages of the total system mass is to avoid side reactions such as epoxy group self-polymerization caused by excessively high local concentrations, ensuring uniform dispersion of GMA and full reaction with the pre-crosslinked network. The core chemical reaction in this step is the epoxy ring-opening nucleophilic addition reaction. The epoxy group in the GMA molecule has ring strain, and the carbon atom on the ring carries a partial positive charge due to the electron-withdrawing effect of the oxygen atom. It is easily attacked by the amino (-NH2) and hydroxyl (-OH) groups remaining in the soy protein isolate and chitosan in the pre-crosslinked network as nucleophiles. The amino group has higher nucleophilic activity and preferentially undergoes ring-opening reaction with the epoxy group to form a β-hydroxyamine structure. At the same time, the hydroxyl group also undergoes ring-opening reaction with the epoxy group to form a β-hydroxy ether structure. Finally, the photosensitive double bond (-C=C-) in the GMA molecule is covalently grafted to the pre-crosslinked network, providing active sites for subsequent photocuring. Holding at 60℃ for 3 hours is to provide the activation energy for the reaction and promote the complete ring-opening reaction.

[0038] ;

[0039] After adding 2% activated carbon for adsorption for 30 minutes, vacuum filtration is performed. This is a physical purification process. The porous structure of activated carbon can adsorb unreacted GMA monomers, reaction byproducts and trace impurities. Vacuum filtration can quickly separate activated carbon from the adhesive, ensuring that the adhesive is clear and transparent and avoiding impurities from affecting the bonding strength and storage stability of the adhesive.

[0040] The subsequent light-shielding operation is to prevent the photoinitiator from decomposing prematurely. Adding 2-5% of water-soluble photoinitiator (such as Irgacure2959) has the core function of absorbing energy under ultraviolet light irradiation, decomposing to generate active free radicals, and initiating the free radical polymerization reaction of the photosensitive double bonds grafted on the pre-crosslinked network to achieve rapid curing of the adhesive.

[0041] The addition of 3-8% hydrophobic nano-silica serves two purposes. First, it forms a uniformly dispersed inorganic reinforcing phase through ultrasonic dispersion. Its hydrophobic surface can fill the gaps in the adhesive network, improving water resistance and mechanical strength. Second, the high specific surface area of ​​the nanoparticles enhances the interfacial bonding force with the pre-crosslinked network, preventing the adhesive layer from cracking. 1-3% plant-derived tannic acid acts as a mildew inhibitor, not only inhibiting mold growth but also forming hydrogen bonds with the amino groups in the pre-crosslinked network through its phenolic hydroxyl groups, thus helping to enhance the crosslinking density. Finally, deionized water is used to adjust the solid content to 30% and control the viscosity to 1500-2500 mPa·s to adapt to the subsequent coating process, ensuring that the adhesive has both good fluidity and can form a uniform adhesive layer on the substrate surface. Through the synergistic effect of photosensitive grafting and functional components, a high-performance adhesive that is formaldehyde-free, water-resistant, mildew-resistant, and photocurable is finally obtained.

[0042] S4. Composite panel forming and post-processing:

[0043] In a light-protected environment, formaldehyde-free adhesive is applied to the upper and lower surfaces of the reinforcing core layer using a double-sided coating method, with an application rate of 180-250 g / m². 2 After applying the adhesive, let it stand in the dark for 10-15 minutes; then stack the waterproof and wear-resistant surface layer, the adhesive-coated reinforcing core layer, and the balancing back layer in sequence, and put them into a hot press. First, hot press at 85-95℃ and 0.9-1.5MPa for 3-5 minutes, then turn on the ultraviolet curing device to simultaneously irradiate the upper and lower surfaces of the composite board for 2-4 minutes to cure. Let it cool naturally to room temperature and age for 12-24 hours. After fine sanding and trimming, and checking the thickness, density, and bonding strength, the high water-resistant formaldehyde-free cabinet composite board is obtained.

[0044] Apply adhesive to both sides in the dark and let it stand for 10-15 minutes. This will not only protect the photoinitiator from premature decomposition, but also allow the adhesive to fully wet each layer of substrate, fill tiny gaps, ensure sufficient interface contact, and prevent adhesive loss.

[0045] After stacking in sequence, hot press at 85-95℃ and 0.9-1.5MPa for 3-5 minutes. The high temperature reduces the viscosity of the adhesive and promotes penetration, while the high pressure compacts the blank to reduce gaps, achieving tight bonding between the layers and strengthening the bond.

[0046] Then, the UV curing device is turned on for synchronous irradiation for 2-4 minutes, which is the core chemical reaction stage of the entire process. The mechanism is a free radical-initiated polymerization and cross-linking reaction: the pre-grafted glycidyl methacrylate in the adhesive contains photosensitive double bonds (-C=C-). After the photoinitiator absorbs the UV light energy, it decomposes to generate active free radicals. The free radicals quickly attack the photosensitive double bonds, initiating the opening of the double bonds and the chain growth reaction. The double bonds on adjacent molecular chains are connected to each other to form a three-dimensional cross-linked polymer network. This covalent cross-linking makes the adhesive layer irreversibly change from a liquid state to a solid state, firmly bonding the waterproof and wear-resistant surface layer, the reinforcing core layer, and the balancing back layer into one. At the same time, the cross-linking network is densified, reducing the water molecule penetration channels and improving the water resistance of the composite board.

[0047] After natural cooling and aging for 12-24 hours, internal stress is released, the cross-linking network is improved, and the interface bonding is strengthened. After fine sanding (smoothing the surface) and trimming (ensuring dimensions), the finished product is obtained after passing inspection. There is no formaldehyde release throughout the process, and it has both high strength and high water resistance.

[0048] Preferably, the viscosity of the pre-crosslinked product is 5000-8000 mPa·s, and the viscosity of the finished formaldehyde-free adhesive is 1500-2500 mPa·s.

[0049] Preferably, the wavelength of the ultraviolet curing device is set to 365nm, and the power is 80-120mW / cm². 2 During the composite board forming and post-processing steps, the aging temperature for 12-24 hours is 23±2℃ and the relative humidity is 50±5%.

[0050] Compared with the prior art, the beneficial effects of the present invention are:

[0051] 1. This invention employs a composite modification method combining soybean protein isolate-chitosan-oxidized starch Schiff base pre-crosslinking and glycidyl methacrylate photosensitive grafting. This method, along with synergistic amino-aldehyde covalent crosslinking, epoxy ring-opening grafting, and UV-initiated polymerization, fundamentally solves the core problems of poor water resistance and insufficient bonding strength in traditional plant protein formaldehyde-free adhesives. This adhesive releases no formaldehyde and, through a dense crosslinked structure and hydrophobic reinforcement, significantly reduces the water absorption rate of the adhesive layer. The bonding strength meets the load-bearing requirements of cabinets, laying the foundation for the core performance of composite boards.

[0052] 2. This invention employs a combination of plasma activation, formaldehyde-free melamine-γ-polyglutamic acid impregnation, silane coupling, and nano-silica reinforced coating. Through the generation of surface active sites, the construction of formaldehyde-free cross-linked networks, and multi-level effects of interfacial covalent bonding, it solves the problems of poor wear resistance, insufficient flame retardancy, and weak bonding with the core layer in traditional surface layers. It achieves multi-functional integration of wear resistance, flame retardancy, high water resistance, and strong adhesion, making it suitable for the high-temperature, humid, and easily scratched environment of the kitchen.

[0053] 3. This invention uses a mixture of poplar fiber and straw, combined with alkali treatment and hydrophobic grafting of alkyl ketone dimers. Through alkali removal of impurities to expose hydroxyl groups and the covalent bonding mechanism of lactone rings, it solves the problems of poor moisture resistance and weak mechanical support in the core layer. Complementary raw materials reduce costs, fiber activation enhances reactivity, and the alkyl ketone dimer constructs a continuous hydrophobic layer. The dense, interwoven structure ensures the long-term load-bearing reliability of the cabinet.

[0054] 4. This invention employs a synergistic process of light-shielding adhesive application and static setting, hot pressing for densification, and simultaneous curing under ultraviolet light. Through thorough wetting of the adhesive combined with physical compaction and rapid cross-linking, it solves the problems of uneven interlayer bonding, low curing efficiency, and high internal stress that easily leads to warping. This improves the interlayer bonding strength and curing efficiency, ensures the dimensional stability of the composite board, and avoids warping and delamination during use. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the layered structure of the cabinet composite board produced by this invention. Detailed Implementation

[0056] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0057] Example 1: Preparation method of high water resistance formaldehyde-free cabinet composite board:

[0058] S1. Preparation of waterproof and wear-resistant surface layer:

[0059] Decorative base paper is activated by plasma, cross-linked with melamine and γ-polyglutamic acid under citric acid catalysis, and then 7% by weight of nano-sized aluminum hydroxide flame retardant is added to prepare a formaldehyde-free impregnation resin with a solid content of 47%. The activated decorative base paper is impregnated in the resin, pre-dried with hot air at 90℃ for 100s, impregnated again, dried at 115℃ for 6min, and finely sanded. A layer of ethanol solution containing γ-methacryloyloxypropyltrimethoxysilane is rolled onto its surface, dried, and then coated with polyurethane acrylate resin doped with 1.5wt% nano-silica. After curing, a thickened melamine board with a thickness of 0.5mm is obtained.

[0060] S2. Preparation of the reinforced core layer:

[0061] Poplar fiber is mixed with crushed straw, sprayed with 5% sodium hydroxide solution, alkali treated at 50℃ for 4 hours, washed until neutral and then pressed to dehydrate; it is then evenly mixed with alkyl ketene dimer waterproofing agent emulsion, laid into a blank, pre-pressed at 180℃ and 2.5MPa for 5 minutes, and sanded to a standard thickness of 15mm and a specified density to obtain an inner waterproof reinforced core layer.

[0062] S3. Preparation of formaldehyde-free adhesive:

[0063] S301, 55 parts of soy protein isolate were prepared into a 15wt% aqueous solution, 12 parts of chitosan were prepared into a 5wt% acetic acid solution, 25 parts of oxidized starch were added to deionized water, and gelatinized at 85℃ for 30 min to obtain starch paste. The mixture was then mixed, and the pH was adjusted to 8.5 with 10% NaOH solution. The mixture was reacted at 55℃ and 350 r / min for 2.5 h to obtain a pre-crosslinked product with a viscosity of 7000 mPa·s.

[0064] S302. Cool the pre-crosslinked product to 40℃, adjust the pH to 7.5 with 5% acetic acid solution, replace with nitrogen twice, add 7.5% glycidyl methacrylate by mass of the total system in three portions, react at 60℃ for 3 hours, add 2% activated carbon for adsorption for 30 minutes, vacuum filter, add 3.5% photoinitiator and 5.5% hydrophobic nano silica under light-protected environment, ultrasonically disperse for 20 minutes, then add 2% tannic acid, adjust the solid content to 30%, control the viscosity to 2000 mPa·s, and obtain the formaldehyde-free adhesive.

[0065] S4. Composite panel forming and post-processing:

[0066] In a light-protected environment, formaldehyde-free adhesive was applied to the upper and lower surfaces of the reinforcing core layer using a double-sided coating method, with an application rate of 180 g / m². 2 After applying the adhesive, let it stand in the dark for 12 minutes. Then, stack the waterproof and wear-resistant surface layer, the adhesive-coated reinforcing core layer, and the balancing back layer in sequence, and put them into a hot press. First, hot press at 90℃ and 1.2MPa for 4 minutes, then turn on the ultraviolet curing device to simultaneously irradiate the upper and lower surfaces of the composite board for 3 minutes to cure. Let it cool naturally to room temperature and age for 18 hours. After fine sanding and trimming, and checking the thickness, density, and bonding strength, the high water resistance formaldehyde-free cabinet composite board is obtained.

[0067] Example 2: Preparation method of high water resistance formaldehyde-free cabinet composite board:

[0068] S1. Preparation of waterproof and wear-resistant surface layer:

[0069] Decorative base paper is activated by plasma, cross-linked with melamine and γ-polyglutamic acid under citric acid catalysis, and then 7% by weight of nano-sized aluminum hydroxide flame retardant is added to prepare a formaldehyde-free impregnation resin with a solid content of 47%. The activated decorative base paper is impregnated in the resin, pre-dried with hot air at 90℃ for 100s, impregnated again, dried at 115℃ for 6min, and finely sanded. A layer of ethanol solution containing γ-methacryloyloxypropyltrimethoxysilane is rolled onto its surface, dried, and then coated with polyurethane acrylate resin doped with 1.5wt% nano-silica. After curing, a thickened melamine board with a thickness of 0.5mm is obtained.

[0070] S2. Preparation of the reinforced core layer:

[0071] Poplar fiber is mixed with crushed straw, sprayed with 5% sodium hydroxide solution, alkali treated at 50℃ for 4 hours, washed until neutral and then pressed to dehydrate; it is then evenly mixed with alkyl ketene dimer waterproofing agent emulsion, laid into a blank, pre-pressed at 180℃ and 2.5MPa for 5 minutes, and sanded to a standard thickness of 15mm and a specified density to obtain an inner waterproof reinforced core layer.

[0072] S3. Preparation of formaldehyde-free adhesive:

[0073] S301, 55 parts of soy protein isolate were prepared into a 15wt% aqueous solution, 12 parts of chitosan were prepared into a 5wt% acetic acid solution, 25 parts of oxidized starch were added to deionized water, and gelatinized at 85℃ for 30 min to obtain starch paste. The mixture was then mixed, and the pH was adjusted to 8.5 with 10% NaOH solution. The mixture was reacted at 55℃ and 350 r / min for 2.5 h to obtain a pre-crosslinked product with a viscosity of 7000 mPa·s.

[0074] S302. Cool the pre-crosslinked product to 40℃, adjust the pH to 7.5 with 5% acetic acid solution, replace with nitrogen twice, add 7.5% glycidyl methacrylate by mass of the total system in three portions, react at 60℃ for 3 hours, add 2% activated carbon for adsorption for 30 minutes, vacuum filter, add 3.5% photoinitiator and 5.5% hydrophobic nano silica under light-protected environment, ultrasonically disperse for 20 minutes, then add 2% tannic acid, adjust the solid content to 30%, control the viscosity to 2000 mPa·s, and obtain the formaldehyde-free adhesive.

[0075] S4. Composite panel forming and post-processing:

[0076] In a light-protected environment, formaldehyde-free adhesive was applied to the upper and lower surfaces of the reinforcing core layer using a double-sided coating method, with an application rate of 250 g / m². 2 After applying the adhesive, let it stand in the dark for 12 minutes. Then, stack the waterproof and wear-resistant surface layer, the adhesive-coated reinforcing core layer, and the balancing back layer in sequence, and put them into a hot press. First, hot press at 90℃ and 1.2MPa for 4 minutes, then turn on the ultraviolet curing device to simultaneously irradiate the upper and lower surfaces of the composite board for 3 minutes to cure. Let it cool naturally to room temperature and age for 18 hours. After fine sanding and trimming, and checking the thickness, density, and bonding strength, the high water resistance formaldehyde-free cabinet composite board is obtained.

[0077] Example 3: Preparation method of high water resistance formaldehyde-free cabinet composite board:

[0078] S1. Preparation of waterproof and wear-resistant surface layer:

[0079] Decorative base paper is activated by plasma, cross-linked with melamine and γ-polyglutamic acid under citric acid catalysis, and then 7% by weight of nano-sized aluminum hydroxide flame retardant is added to prepare a formaldehyde-free impregnation resin with a solid content of 47%. The activated decorative base paper is impregnated in the resin, pre-dried with hot air at 90℃ for 100s, impregnated again, dried at 115℃ for 6min, and finely sanded. A layer of ethanol solution containing γ-methacryloyloxypropyltrimethoxysilane is rolled onto its surface, dried, and then coated with polyurethane acrylate resin doped with 1.5wt% nano-silica. After curing, a thickened melamine board with a thickness of 0.5mm is obtained.

[0080] S2. Preparation of the reinforced core layer:

[0081] Poplar fiber is mixed with crushed straw, sprayed with 5% sodium hydroxide solution, alkali treated at 50℃ for 4 hours, washed until neutral and then pressed to dehydrate; it is then evenly mixed with alkyl ketene dimer waterproofing agent emulsion, laid into a blank, pre-pressed at 180℃ and 2.5MPa for 5 minutes, and sanded to a standard thickness of 15mm and a specified density to obtain an inner waterproof reinforced core layer.

[0082] S3. Preparation of formaldehyde-free adhesive:

[0083] S301, 55 parts of soy protein isolate were prepared into a 15wt% aqueous solution, 12 parts of chitosan were prepared into a 5wt% acetic acid solution, 25 parts of oxidized starch were added to deionized water, and gelatinized at 85℃ for 30 min to obtain starch paste. The mixture was then mixed, and the pH was adjusted to 8.5 with 10% NaOH solution. The mixture was reacted at 55℃ and 350 r / min for 2.5 h to obtain a pre-crosslinked product with a viscosity of 7000 mPa·s.

[0084] S302. Cool the pre-crosslinked product to 40℃, adjust the pH to 7.5 with 5% acetic acid solution, replace with nitrogen twice, add 7.5% glycidyl methacrylate by mass of the total system in three portions, react at 60℃ for 3 hours, add 2% activated carbon for adsorption for 30 minutes, vacuum filter, add 3.5% photoinitiator and 5.5% hydrophobic nano silica under light-protected environment, ultrasonically disperse for 20 minutes, then add 2% tannic acid, adjust the solid content to 30%, control the viscosity to 2000 mPa·s, and obtain the formaldehyde-free adhesive.

[0085] S4. Composite panel forming and post-processing:

[0086] In a light-protected environment, formaldehyde-free adhesive was applied to the upper and lower surfaces of the reinforcing core layer using a double-sided coating method, with an application rate of 215 g / m². 2After applying the adhesive, let it stand in the dark for 12 minutes. Then, stack the waterproof and wear-resistant surface layer, the adhesive-coated reinforcing core layer, and the balancing back layer in sequence, and put them into a hot press. First, hot press at 90℃ and 1.2MPa for 4 minutes, then turn on the ultraviolet curing device to simultaneously irradiate the upper and lower surfaces of the composite board for 3 minutes to cure. Let it cool naturally to room temperature and age for 18 hours. After fine sanding and trimming, and checking the thickness, density, and bonding strength, the high water resistance formaldehyde-free cabinet composite board is obtained.

[0087] Example 4: Preparation method of high water resistance formaldehyde-free cabinet composite board:

[0088] S1. Preparation of waterproof and wear-resistant surface layer:

[0089] Decorative base paper is activated by plasma, cross-linked with melamine and γ-polyglutamic acid under citric acid catalysis, and then 7% by weight of nano-sized aluminum hydroxide flame retardant is added to prepare a formaldehyde-free impregnation resin with a solid content of 47%. The activated decorative base paper is impregnated in the resin, pre-dried with hot air at 90℃ for 100s, impregnated again, dried at 115℃ for 6min, and finely sanded. A layer of ethanol solution containing γ-methacryloyloxypropyltrimethoxysilane is rolled onto its surface, dried, and then coated with polyurethane acrylate resin doped with 1.5wt% nano-silica. After curing, a thickened melamine board with a thickness of 0.5mm is obtained.

[0090] S2. Preparation of the reinforced core layer:

[0091] Poplar fiber is mixed with crushed straw, sprayed with 5% sodium hydroxide solution, alkali treated at 50℃ for 4 hours, washed until neutral and then pressed to dehydrate; it is then evenly mixed with alkyl ketene dimer waterproofing agent emulsion, laid into a blank, pre-pressed at 180℃ and 2.5MPa for 5 minutes, and sanded to a standard thickness of 15mm and a specified density to obtain an inner waterproof reinforced core layer.

[0092] S3. Preparation of formaldehyde-free adhesive:

[0093] S301, 55 parts of soy protein isolate were prepared into a 15wt% aqueous solution, 12 parts of chitosan were prepared into a 5wt% acetic acid solution, 25 parts of oxidized starch were added to deionized water, and gelatinized at 85℃ for 30 min to obtain starch paste. The mixture was then mixed, and the pH was adjusted to 8.5 with 10% NaOH solution. The mixture was reacted at 55℃ and 350 r / min for 2.5 h to obtain a pre-crosslinked product with a viscosity of 7000 mPa·s.

[0094] S302. Cool the pre-crosslinked product to 40℃, adjust the pH to 7.5 with 5% acetic acid solution, replace with nitrogen twice, add 5% glycidyl methacrylate by mass in three portions, react at 60℃ for 3 hours, add 2% activated carbon for adsorption for 30 minutes, vacuum filter, add 3.5% photoinitiator and 5.5% hydrophobic nano silica under light-protected environment, ultrasonically disperse for 20 minutes, add 2% tannic acid, adjust the solid content to 30%, control the viscosity to 2000 mPa·s, and obtain formaldehyde-free adhesive.

[0095] S4. Composite panel forming and post-processing:

[0096] In a light-protected environment, formaldehyde-free adhesive was applied to the upper and lower surfaces of the reinforcing core layer using a double-sided coating method, with an application rate of 215 g / m². 2 After applying the adhesive, let it stand in the dark for 12 minutes. Then, stack the waterproof and wear-resistant surface layer, the adhesive-coated reinforcing core layer, and the balancing back layer in sequence, and put them into a hot press. First, hot press at 90℃ and 1.2MPa for 4 minutes, then turn on the ultraviolet curing device to simultaneously irradiate the upper and lower surfaces of the composite board for 3 minutes to cure. Let it cool naturally to room temperature and age for 18 hours. After fine sanding and trimming, and checking the thickness, density, and bonding strength, the high water resistance formaldehyde-free cabinet composite board is obtained.

[0097] Example 5: Preparation method of high water resistance formaldehyde-free cabinet composite board:

[0098] S1. Preparation of waterproof and wear-resistant surface layer:

[0099] Decorative base paper is activated by plasma, cross-linked with melamine and γ-polyglutamic acid under citric acid catalysis, and then 7% by weight of nano-sized aluminum hydroxide flame retardant is added to prepare a formaldehyde-free impregnation resin with a solid content of 47%. The activated decorative base paper is impregnated in the resin, pre-dried with hot air at 90℃ for 100s, impregnated again, dried at 115℃ for 6min, and finely sanded. A layer of ethanol solution containing γ-methacryloyloxypropyltrimethoxysilane is rolled onto its surface, dried, and then coated with polyurethane acrylate resin doped with 1.5wt% nano-silica. After curing, a thickened melamine board with a thickness of 0.5mm is obtained.

[0100] S2. Preparation of the reinforced core layer:

[0101] Poplar fiber is mixed with crushed straw, sprayed with 5% sodium hydroxide solution, alkali treated at 50℃ for 4 hours, washed until neutral and then pressed to dehydrate; it is then evenly mixed with alkyl ketene dimer waterproofing agent emulsion, laid into a blank, pre-pressed at 180℃ and 2.5MPa for 5 minutes, and sanded to a standard thickness of 15mm and a specified density to obtain an inner waterproof reinforced core layer.

[0102] S3. Preparation of formaldehyde-free adhesive:

[0103] S301, 55 parts of soy protein isolate were prepared into a 15wt% aqueous solution, 12 parts of chitosan were prepared into a 5wt% acetic acid solution, 25 parts of oxidized starch were added to deionized water, and gelatinized at 85℃ for 30 min to obtain starch paste. The mixture was then mixed, and the pH was adjusted to 8.5 with 10% NaOH solution. The mixture was reacted at 55℃ and 350 r / min for 2.5 h to obtain a pre-crosslinked product with a viscosity of 7000 mPa·s.

[0104] S302. Cool the pre-crosslinked product to 40℃, adjust the pH to 7.5 with 5% acetic acid solution, replace with nitrogen twice, add 10% glycidyl methacrylate by mass of the total system in three portions, react at 60℃ for 3 hours, add 2% activated carbon for adsorption for 30 minutes, vacuum filter, add 3.5% photoinitiator and 5.5% hydrophobic nano silica under light-protected environment, ultrasonically disperse for 20 minutes, then add 2% tannic acid, adjust the solid content to 30%, control the viscosity to 2000 mPa·s, and obtain the formaldehyde-free adhesive.

[0105] S4. Composite panel forming and post-processing:

[0106] In a light-protected environment, formaldehyde-free adhesive was applied to the upper and lower surfaces of the reinforcing core layer using a double-sided coating method, with an application rate of 215 g / m². 2 After applying the adhesive, let it stand in the dark for 12 minutes. Then, stack the waterproof and wear-resistant surface layer, the adhesive-coated reinforcing core layer, and the balancing back layer in sequence, and put them into a hot press. First, hot press at 90℃ and 1.2MPa for 4 minutes, then turn on the ultraviolet curing device to simultaneously irradiate the upper and lower surfaces of the composite board for 3 minutes to cure. Let it cool naturally to room temperature and age for 18 hours. After fine sanding and trimming, and checking the thickness, density, and bonding strength, the high water resistance formaldehyde-free cabinet composite board is obtained.

[0107] Comparative Example 1:

[0108] Compared to Example 3, in Comparative Example 1, the formaldehyde-free adhesive was applied to the upper and lower surfaces of the reinforcing core layer at an application rate of 280 g / m². 2 All other conditions remain unchanged.

[0109] Comparative Example 2:

[0110] Compared with Example 3, in Comparative Example 2, the amount of glycidyl methacrylate added was 13% of the total system mass when preparing the formaldehyde-free adhesive, while other conditions remained unchanged.

[0111] Comparative Example 3:

[0112] Compared with Example 3, no glycidyl methacrylate was added when preparing the formaldehyde-free adhesive in Comparative Example 3, and other conditions remained unchanged.

[0113] Comparative Example 4:

[0114] Compared with Example 3, in Comparative Example 4, the waterproof and wear-resistant surface layer was not prepared by roller coating with an ethanol solution containing γ-methacryloxypropyltrimethoxysilane, while other conditions remained unchanged.

[0115] Comparative Example 5:

[0116] Compared with Example 3, the polyurethane acrylate resin in Comparative Example 5 was not doped with nano-silica, while other conditions remained unchanged.

[0117] Comparative Example 6:

[0118] Compared with Example 3, no alkyl ketene dimer waterproofing agent emulsion was added to the core layer in Comparative Example 6, while other conditions remained unchanged.

[0119] Comparative Example 7:

[0120] Compared with Example 3, the decorative base paper in Comparative Example 7 was not subjected to plasma activation, while other conditions remained unchanged.

[0121] Performance testing:

[0122] 1. In accordance with the standard test methods in GB / T17657-1999 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels" and GB / T29899-2013 "Test Methods for Formaldehyde Emission and Volatile Organic Compound (VOC) Emission of Wood-based Panels and Their Products", the present invention was tested for formaldehyde emission, static bending strength, modulus of elasticity, 24-hour water absorption thickness swelling rate, surface abrasion resistance, interlayer bonding strength, and VOC emission.

[0123] 2. Resistance to damp heat aging

[0124] 1) Test steps:

[0125] Specimens were prepared according to GB / T17657-1999. The initial static bending strength (σ0) and water absorption thickness expansion rate (TS0) of the specimens were measured. The specimens were then placed in a constant temperature and humidity chamber and the cyclic conditions were set as follows: 40℃, 90% relative humidity for 12h → 60℃, 30% relative humidity for 12h. One cycle was completed, and a total of 5 cycles were performed. The specimens were then removed and allowed to cool naturally to room temperature (23±2℃). The static bending strength (σ1) and water absorption thickness expansion rate (TS1) after treatment were measured.

[0126] 2) Calculation formula:

[0127] Static bending strength retention rate: Rσ=σ1 / σ0×100%, where Rσ is the static bending strength retention rate (%), σ0 is the initial static bending strength (MPa), and σ1 is the static bending strength after damp heat cycling (MPa).

[0128] Water absorption thickness expansion rate change rate: ΔTS=TS1-TS0, where: ΔTS is the change value of water absorption thickness expansion rate (%), TS0 is the initial water absorption thickness expansion rate (%), and TS1 is the water absorption thickness expansion rate (%) after wet heat cycle.

[0129] Table 1. Basic physicochemical data of composite plates prepared in the examples and comparative examples.

[0130]

[0131] Table 2 shows the performance stability data of the composite plates prepared in the examples and comparative examples.

[0132]

[0133] Figure 1 This is a schematic diagram of the layered structure of the cabinet composite board produced by this invention. From top to bottom, it consists of five layers: the outermost layer is a waterproof and wear-resistant surface layer, which is the surface layer used in direct contact and bears the functions of wear resistance, waterproofing, and decoration; below the surface layer and below the middle layer are formaldehyde-free adhesive layers, which serve to bond the layers together and ensure the formaldehyde-free and environmentally friendly characteristics of the board; the middle layer is a reinforcing core layer, which is the mechanical core of the board, providing the strength required for load-bearing and also has internal waterproofing capabilities; the bottom layer is a balancing back layer, which is used to offset the stress difference between the surface layer and the core layer, preventing the board from warping or deforming during use and ensuring structural stability.

[0134] In Example 3, the core parameters such as the amount of adhesive applied and the amount of glycidyl methacrylate were within the optimal range, and the components and processes formed a synergistic effect. Mechanistically, the appropriate amount of adhesive applied ensured that the adhesive layer uniformly covered the interface without excess adhesive accumulation. The grafting rate of glycidyl methacrylate matched the pre-crosslinked network, ensuring sufficient photosensitive double bond density while avoiding excessive crosslinking that would generate internal stress. The adhesive layer was sufficiently wetted and penetrated into the core layer and the surface layer. The Schiff base crosslinked network and the photosensitive polymer network were dense and continuous. At the same time, the hydrophobic layer of the core layer waterproofing agent and the silane coupling effect of the surface layer worked synergistically. Finally, according to the data in Tables 1 and 2, the overall performance was optimal.

[0135] Compared to Example 3, the mechanical properties and water resistance data of the composite board in Example 1 showed a slight decline. The main reason is that the amount of adhesive applied was lower than the optimal range, resulting in insufficient adhesive layer thickness. Although basic bonding could be achieved, it could not completely fill the tiny voids on the substrate surface, reducing the interfacial contact area. At the same time, the dispersion continuity of hydrophobic nano-silica in the adhesive layer was affected, the density of the cross-linked network was slightly weaker, and the water molecule penetration resistance and interlayer cohesion decreased slightly, resulting in a slight fluctuation in performance compared to Example 3.

[0136] Compared to Example 3, Example 2 showed some improvement in mechanical properties, but slight fluctuations in water resistance and environmental protection indicators. Mechanistically, the higher adhesive application rate compared to Example 3 resulted in a thicker adhesive layer, increasing the interlayer bonding area and strengthening the internal adhesion. However, excess adhesive was difficult to completely remove during hot-press curing, leading to localized adhesive layer accumulation in some areas. This resulted in residual micropores after curing, and the excess adhesive prolonged the completion of the cross-linking reaction, causing the water resistance and VOC emission indicators to not reach the balanced levels of Example 3.

[0137] Compared to Example 3, Comparative Example 1 showed a significant decline in several properties, especially mechanical properties and resistance to damp heat. The key issue was that the amount of adhesive applied far exceeded the suitable range. The excessively thick adhesive layer caused excess adhesive to overflow during hot pressing, resulting in waste and compromising the interfacial bonding accuracy between the core layer and the surface layer. Furthermore, during UV curing, the excessively thick adhesive layer could not receive sufficient light internally, leading to incomplete cross-linking and a loose adhesive layer structure. This resulted in concentrated internal stress and a discontinuous hydrophobic network, ultimately causing a significant deterioration in overall performance.

[0138] Compared to Example 3, Example 4 showed a slight decrease in mechanical properties and water resistance. The core reason was that the amount of glycidyl methacrylate was lower than the suitable range, resulting in insufficient photosensitive double bond grafting density. This led to poor density of the crosslinked network formed during photocuring and increased porosity within the adhesive layer. At the same time, the effect of glycidyl methacrylate as a crosslinking bridging agent was weakened, failing to fully enhance the interfacial bonding between the pre-crosslinked network and the functional filler. Consequently, the water molecule penetration resistance and interlayer cohesion decreased, resulting in a slight decline in performance.

[0139] Compared with Example 3, Example 5 shows an improved trend in all performance aspects. Mechanistically, the optimal dosage of glycidyl methacrylate significantly increases the density of photosensitive double bonds on the pre-crosslinked network, enabling the formation of a denser, continuous three-dimensional crosslinked network during UV curing. This network not only enhances the mechanical support of the adhesive layer but also further blocks water molecule penetration channels. Simultaneously, it works synergistically with hydrophobic nano-silica, resulting in superior water resistance and structural stability, thus upgrading the overall performance.

[0140] Compared to Example 3, the overall performance of Comparative Example 2 declined significantly. The key issue was that the amount of glycidyl methacrylate used far exceeded the reasonable range. Excessive glycidyl methacrylate is prone to self-polymerization, forming free polymer particles that interfere with the effective bonding with the pre-crosslinked network. This results in an uneven crosslinked network with internal stress concentration points, leading to a decrease in the density of the adhesive layer, simultaneous deterioration in mechanical strength and water resistance, and slight fluctuations in environmental indicators.

[0141] The mechanical properties, water resistance, and damp heat stability of Comparative Example 3 showed a significant decline compared to Example 3, and the surface abrasion resistance also decreased substantially. The core mechanism is that without the addition of glycidyl methacrylate, the pre-crosslinked network lacks photosensitive double bond grafting sites, making it impossible to form a dense three-dimensional crosslinked network through UV curing. The adhesive layer relies solely on the initial Schiff base crosslinking, resulting in a loose structure and insufficient cohesion. At the same time, the strengthening effect of GMA on the network is lost, making it easy for water molecules to penetrate and resulting in weak interlayer bonding, ultimately leading to the deterioration of various core properties.

[0142] Comparative Example 4 showed a significant decline in interlayer bond strength and surface abrasion resistance, while other properties fluctuated but the magnitude was small. The key reason is the lack of silane coupling agent roll coating, resulting in a lack of Si-OC covalent bonds between the top layer and the adhesive layer. The bonding relies solely on physical adsorption and hydrogen bonding, significantly weakening the interfacial forces. The absence of silane also leads to decreased compatibility between the top layer resin and the adhesive layer, making it prone to micro-gaps at the interface after curing, which in turn affects the reliability of interlayer adhesion and the durability of surface abrasion resistance.

[0143] According to the data in Tables 1 and 2, Comparative Example 5 exhibited the worst surface abrasion resistance, while its other properties were similar to the standard example but slightly lower. Mechanistically, the polyurethane acrylate resin lacked nano-silica doping, resulting in insufficient inorganic reinforcing phase to fill the resin network voids. This led to insufficient resin layer density and a significant reduction in surface hardness and scratch resistance. The hydrophobic synergistic effect of nano-silica disappeared, which, while not significantly affecting overall water resistance, slightly reduced localized surface water resistance and mechanical support.

[0144] In Comparative Example 6, the 24-hour water absorption thickness swelling rate and the ΔTS value after damp heat aging increased sharply, and the mechanical properties and stability also declined significantly. The core problem is that no waterproofing agent was added to the core layer, and the cellulose surface lacked a continuous hydrophobic layer, allowing water molecules to easily penetrate through the fiber gaps. At the same time, the waterproofing agent lacked the cross-linking and densifying effect on the fibers, resulting in a loose core layer structure that easily absorbs water and swells in humid environments. This leads to a significant deterioration in overall water resistance and structural stability, making it unsuitable for the humid environment of a kitchen.

[0145] Comparative Example 7 showed a significant decrease in surface adhesion, surface abrasion resistance, and interlayer bonding strength. Mechanistically, the decorative base paper was not activated by plasma, resulting in a small number of surface-active functional groups and insufficient roughness. This made it difficult for the impregnating resin to fully penetrate and bond, leading to weak interfacial forces between the resin and the base paper fibers. Consequently, the contact area and bonding strength between the subsequent coating layer and the substrate were also affected, making it prone to surface peeling and abrasion resistance degradation after curing, thus reducing the overall reliability of the interfacial bonding.

[0146] The above embodiments and comparative examples demonstrate that the superior performance of the composite board of the present invention depends on the appropriate matching of parameters such as the amount of adhesive applied and the amount of glycidyl methacrylate, as well as the synergistic effect of key components such as glycidyl methacrylate, waterproofing agent, silane coupling agent, and nano-silica with the plasma activation process. These factors directly affect the mechanical properties, water resistance, and stability of the product by regulating the density of the crosslinking network, interfacial bonding force, and hydrophobic structure. The lack or overuse of core components, or deviation from optimal parameters, will lead to performance degradation, verifying the scientific nature and synergistic advantages of the technical solution of the present invention.

[0147] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A highly water-resistant, formaldehyde-free cabinet composite board, characterized in that, From top to bottom, they include: Waterproof and wear-resistant surface layer: This is a thickened melamine board with a thickness of 0.1-0.8 mm. The preparation steps of the thickened melamine board are as follows: Decorative base paper is activated by plasma, cross-linked with melamine and γ-polyglutamic acid under citric acid catalysis, and then 5-8% of nano-sized aluminum hydroxide flame retardant is added to prepare a formaldehyde-free impregnation resin with a solid content of 45-50%. The treated decorative base paper is impregnated in the resin, pre-dried in hot air at 85-95℃ for 1.5-2 minutes, impregnated again, dried at 110-120℃ for 6 minutes, finely sanded, and then a layer of ethanol solution containing γ-methacryloyloxypropyltrimethoxysilane is rolled onto its surface. After drying, a polyurethane acrylate resin doped with 1.0-2.0 wt% nano-silica is coated and cured to obtain a thickened melamine board. Reinforcing core layer: a mixture of alkali-treated wood fiber and crop straw, with added alkyl ketene dimer waterproofing agent, and a thickness of 14.6-15.6 mm; Balanced backing: Waterproof kraft paper, 0.1-0.3mm thick; The three-layer structure is bonded together using a self-made formaldehyde-free adhesive. The preparation steps of the self-made formaldehyde-free adhesive are as follows: T1. Raw material pretreatment: 50-60 parts of soy protein isolate were prepared into a 15wt% protein aqueous solution, 10-15 parts of chitosan were prepared into a 5wt% chitosan acetate solution, and 20-30 parts of oxidized starch were gelatinized at 85℃ for 30min. T2, Pre-crosslinking reaction: Mix the raw materials in S1, adjust the pH to 8.5 with 10% NaOH solution, and react at 55℃ and 300-400 r / min for 2.5 h; T3, Grafting of photosensitive groups: Cool the pre-crosslinked product in S2 to 40℃, adjust the pH to 7.5, purge with nitrogen twice, add glycidyl methacrylate (5-10% of the total mass) in three portions, react at 60℃ for 3 hours, and filter after adsorption with activated carbon. T4. Finished Product Preparation: Add 2-5% photoinitiator, 3-8% hydrophobic nano-silica, and 1-3% tannic acid to the light-protected system, sonicate for 20 minutes, adjust the solid content to 30%, and obtain a formaldehyde-free adhesive.

2. The high water resistance formaldehyde-free cabinet composite board according to claim 1, characterized in that, The steps for preparing the reinforced core layer are as follows: Poplar fiber is mixed with crushed straw, sprayed with 5% sodium hydroxide solution, alkali treated at 50℃ for 4 hours, washed until neutral, pressed and dehydrated, and evenly mixed with alkyl ketone dimer waterproofing agent emulsion. It is then laid into a blank, pre-pressed at 180℃ and 2.5MPa for 5 minutes, and sanded to the standard thickness and density to obtain the inner waterproof reinforced core layer.

3. The high water resistance formaldehyde-free cabinet composite board according to claim 1, characterized in that, The viscosity of the pre-crosslinked product in T2 is 5000-8000 mPa·s, the viscosity of the finished formaldehyde-free adhesive is 1500-2500 mPa·s, and the application rate of the self-made formaldehyde-free adhesive in the preparation of composite boards is 180-250 g / m². 2 Furthermore, it employs a double-sided adhesive coating method.

4. A method for preparing a high water-resistant formaldehyde-free cabinet composite board according to any one of claims 1-3, characterized in that, Includes the following steps: S1 material preparation: Prepare a waterproof and wear-resistant surface layer, a reinforcing core layer, and a self-made formaldehyde-free adhesive. Select waterproof kraft paper with the required thickness for the balancing back layer. S2. Applying adhesive: In a dark environment, the self-made formaldehyde-free adhesive is evenly applied to the upper and lower surfaces of the reinforcing core layer using a double-sided coating method. After coating, the adhesive is left to stand in the dark for 10-15 minutes. S3, Composite: The waterproof and wear-resistant surface layer, the adhesive-coated reinforcing core layer, and the balancing back layer are stacked in sequence and then sent into a hot press. S4. Hot pressing-photocuring composite molding: First, hot press at 85-95℃ and 0.9-1.5MPa for 3-5 minutes, then turn on the ultraviolet curing device to simultaneously irradiate the upper and lower surfaces of the composite board for 2-4 minutes to complete the bonding and shaping. S5. Post-processing: After the molded composite board is naturally cooled to room temperature and aged for 12-24 hours, it is finely sanded, trimmed, and its thickness, density, and bonding strength are inspected to obtain a finished product of high water resistance and formaldehyde-free cabinet composite board.

5. The method for preparing a high water-resistant formaldehyde-free cabinet composite board according to claim 4, characterized in that, In step S4, the wavelength of the ultraviolet curing device is set to 365nm, and the power is 80-120mW / cm². 2 The temperature during the aging process in S5 for 12-24 hours is 23±2℃ and the relative humidity is 50±5%.

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