An antibacterial coating for plywood and a method for preparing the same

Abstract

The present application relates to the technical field of antibacterial coating, in particular to an antibacterial coating for plywood and a preparation method thereof.The present application overcomes the problems of poor adhesion and poor antibacterial durability of the antibacterial coating and the plywood; a polyurethane solution is obtained through prepolymerization and chain extension, a hydrolyzed fluorine-containing silane solution is used for end capping treatment, a quaternary ammonium salt is loaded on nano ceramic, the nano ceramic is connected to the polyurethane through a chemical bond, and a coupling agent is used for crosslinking to obtain the antibacterial coating. Through adjustment of the raw materials and the preparation method, the coating has good adhesion to the plywood; and the nano ceramic has a slow-release effect on the antibacterial quaternary ammonium salt, and together with nano silver, it has a long-lasting antibacterial effect, and even after repeated washing, the antibacterial effect is still good.

Description

Technical Field

[0001] This invention relates to the field of antibacterial coating technology, specifically to an antibacterial coating for plywood and its preparation method. Background Technology

[0002] Plywood, a type of engineered wood product made by gluing together multiple layers of thin veneer, is widely used in furniture, construction, and packaging due to its high strength, good stability, and ease of processing. However, in environments with high humidity or strict hygiene requirements, plywood is prone to bacterial and fungal growth, limiting its application. Therefore, developing antibacterial coatings has become an important research direction for improving the functionality of plywood. In existing technologies, antibacterial coatings on plywood surfaces mainly use organic polymers or inorganic materials such as nano-titanium dioxide as the matrix, incorporating antibacterial agents to achieve the antibacterial effect. Common preparation methods include spraying, dip coating, chemical grafting, and UV curing.

[0003] In existing technologies, polyurethane coatings are widely used due to their excellent adhesion and abrasion resistance, but traditional solvent-based polyurethanes suffer from high volatile organic compound emissions. Waterborne polyurethane is gaining attention as an environmentally friendly alternative, but its durability and antibacterial effects still need optimization. Nano-silver has been extensively studied for its broad-spectrum antibacterial properties, and it is embedded in coatings through physical doping or chemical grafting, but it is prone to loss over time, resulting in insufficient antibacterial durability. Photocatalytic antibacterial agents have self-cleaning functions, but require ultraviolet light irradiation, limiting their indoor application. Natural antibacterial agents such as chitosan are environmentally friendly, but their antibacterial effects are weak and difficult to meet high standards.

[0004] Furthermore, siloxane coatings, as an emerging antibacterial coating substrate, have attracted attention due to their excellent weather resistance, hydrophobicity, and chemical stability. Siloxanes can enhance the fixation effect of antibacterial agents and improve the antifouling performance of the coating by forming flexible and durable coatings; however, the adhesion of siloxane coatings to plywood surfaces is poor, requiring surface modification or the addition of coupling agents for improvement. In addition, the hydrophobicity of siloxane coatings may affect the uniform dispersion of antibacterial agents, leading to unstable antibacterial effects. Existing technologies generally suffer from poor adhesion between the coating and the plywood substrate, especially on rough or waxy plywood surfaces, where the coating is prone to peeling, affecting its service life. Meanwhile, insufficient antibacterial durability remains a key issue; antibacterial agents are easily lost due to friction or washing, limiting the long-term application effect of the coating.

[0005] To address the shortcomings of existing technologies, there is an urgent need to develop an antibacterial coating based on waterborne polyurethane and incorporating the advantages of siloxanes. By optimizing antibacterial agents and adding reactive substances containing silicon and fluorine, the problems of poor adhesion between the coating and plywood and insufficient antibacterial durability can be solved, while maintaining environmental friendliness and low cost.

[0006] To this end, an antibacterial coating for plywood and its preparation method are proposed. Summary of the Invention

[0007] The present invention aims to provide an antibacterial coating for plywood and its preparation method. A polyurethane solution is obtained through a prepolymerization and chain extension reaction, followed by end-capping treatment using a hydrolyzed fluorinated silane solution, and then a quaternary ammonium salt is loaded onto nano-ceramics. The nano-ceramics are chemically bonded to the polyurethane, and finally, a coupling agent is used for cross-linking to obtain the antibacterial coating. Adjustments to the raw materials and preparation method result in good adhesion of the coating to the plywood; the nano-ceramics exhibit a sustained-release effect on the antibacterial quaternary ammonium salt, working in conjunction with nano-silver to achieve a long-lasting antibacterial effect, maintaining good antibacterial performance even after repeated washing.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing an antibacterial coating for plywood, the method being as follows: After cooling polyurethane solution A, perfluorooctyltriethoxysilane solution B is added dropwise to polyurethane solution A to form fluorosilicone-terminated polyurethane. Modified quaternary ammonium salt supported nano-ceramics are added to the fluorosilicone-terminated polyurethane, and the reaction is stirred. Finally, coupling agent and catalyst are added, and the reaction is carried out after heating and depressurization to obtain the end-terminated polyurethane. Nano-silver, modified quaternary ammonium salt-supported nano-ceramics, polyvinylpyrrolidone, and defoamer were added to end-capped polyurethane, along with deionized water. After stirring, the viscosity was adjusted to obtain an antibacterial coating for plywood. The addition of deionized water brought the viscosity of the antibacterial coating to 100-150 mPa·s. By adding the nano-ceramics in stages, agglomeration was reduced, ensuring uniform distribution of quaternary ammonium salt and nano-silver, while also ensuring complete reaction.

[0009] Polyurethane A solution is obtained through prepolymerization and chain extension reactions; Modified quaternary ammonium salt-supported nanoceramics were obtained by loading quaternary ammonium salts onto nano-calcium phosphate ceramics prepared by the sol-gel method.

[0010] Preferably, the prepolymerization reaction process is as follows: under nitrogen protection, 1,4-butanediol and 4,4'-methylenebis(phenyl isocyanate) are added, and the mixture is heated and stirred to react.

[0011] Preferably, the chain extension reaction process is as follows: the prepolymer obtained by the prepolymerization reaction is cooled down, sodium 2,4-diaminobenzenesulfonate solution is added and stirred to react, N,N-dimethylformamide is added to dilute the viscosity, isophorone diisocyanate is added, and the temperature is raised to react.

[0012] The preferred method for preparing perfluorooctyltriethoxysilane solution B is as follows: perfluorooctyltriethoxysilane is added to ethanol and deionized water, hydrochloric acid is added to carry out a hydrolysis reaction, and after the reaction is completed, the solution is filtered, dried, and redissolved to obtain perfluorooctyltriethoxysilane solution B.

[0013] Preferably, the sol-gel method is as follows: calcium nitrate and triethyl phosphate are added to ethanol to form a homogeneous solution; hydrochloric acid is added to the homogeneous solution to hydrolyze and condense to obtain a gel, which is then dried to obtain a dry gel; the dry gel is calcined after being subjected to programmed temperature rise to obtain nano-calcium phosphate ceramics.

[0014] Preferably, the programmed temperature rise conditions are as follows: starting from 80°C, the temperature is increased to 150-220°C at a rate of 5°C / min, held for 15-40 minutes, and then increased to 450-600°C for sintering for 1 hour.

[0015] Preferably, the process of loading quaternary ammonium salt is as follows: disperse nano-calcium phosphate ceramics in ethanol, add dodecyl dimethyl ammonium chloride and γ-aminopropyltriethoxysilane, stir at room temperature, centrifuge, wash and dry.

[0016] This invention also provides an antibacterial coating for plywood, which is prepared by any of the above preparation methods; the raw materials for preparing the antibacterial coating include polyurethane liquid A, perfluorooctyltriethoxysilane liquid B, and quaternary ammonium salt supported nano-ceramics; the viscosity of the antibacterial coating is 100-150 mPa·s; the method of using the antibacterial coating on plywood is as follows: the surface of the plywood is pretreated by sanding with sandpaper to remove surface wax and impurities, and then wiped clean with ethanol; the antibacterial coating is uniformly sprayed onto the surface of the plywood using a spraying process, with the coating thickness controlled at 30-50 μm; finally, it is placed in a 60℃ oven for curing for 30 min, and then allowed to cure naturally at room temperature to obtain a dry antibacterial coating.

[0017] The information on the substances involved is as follows: γ-aminopropyltriethoxysilane (KH-550) has a CAS number of 919-30-2; dibutyltin dilaurate (DBTDL) has a CAS number of 77-58-7; 1,4-butanediol has a CAS number of 110-63-4; 4,4'-methylenebis(phenyl isocyanate) has a CAS number of 101-68-8; sodium 2,4-diaminobenzenesulfonate has a CAS number of 3177-22-8; and isophorone diisocyanate has a CAS number of 4098-71-9. The CAS numbers for perfluorooctyltriethoxysilane, calcium nitrate, and polyvinyl chloride are as follows: 51851-37-7; 10124-37-5; 144026-79-9; 78-40-0; 7173-51-5; 9003-39-8; and BYK-028 polysiloxane defoamer, purchased from BYK Chemicals (Germany), with a density of 0.92 g / cm³. 3 .

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By controlling each reaction stage in the polyurethane preparation process, the adhesion of the antibacterial coating to plywood is significantly improved. The prepolymerization stage controls the reaction ratio and conditions to generate a prepolymer with active NCO groups at both ends, providing sufficient sites for subsequent reactions and imparting suitable flexibility and mechanical strength to the coating. The chain extension stage introduces specific groups, enhancing both the mechanical strength of the coating and its affinity to the plywood surface. The end-capping and crosslinking processes enhance the degree of crosslinking through the synergistic reaction of multiple components, achieving chemical bonding between the coating and the substrate. This ensures stable adhesion of the coating to the plywood surface, preventing peeling even if the substrate deforms, fundamentally guaranteeing the coating's adhesion performance to the plywood.

[0019] 2. The prepared antibacterial coating has a good hydrophobic effect on plywood. Hydrolyzed perfluorooctyltriethoxysilane participates in the end-capping reaction, and its silicon and fluorine elements can enhance the hydrophobicity of the coating. KH-550, as a coupling agent, can promote cross-linking to improve the density of the coating and reduce the water penetration channels. Together, they reduce the adhesion and penetration of water on the coating surface. Reasonable adjustment of the preparation method also enables the effective combination of hydrophobic components, thereby stabilizing and maintaining the hydrophobic effect of the coating.

[0020] 3. The introduction of nano-silver, whose released silver ions have an inhibitory effect on bacterial growth; the addition of quaternary ammonium salt-loaded nano-ceramics, the slow-release quaternary ammonium salt contributes to the antibacterial durability; at the same time, the cross-linking reaction increases the coating density, forming a physical barrier to prevent bacteria from penetrating into the plywood; through the synergistic effect of chemical sterilization and physical barrier, the antibacterial performance of the coating is effectively improved.

[0021] 4. Through rational design, the coating is guaranteed to have long-lasting antibacterial properties; the high specific surface area of ​​nano-ceramics provides attachment sites for quaternary ammonium salts, enabling them to be released slowly; nano-silver can also continuously release silver ions to maintain bactericidal ability; cross-linking reaction enhances the structural stability of the coating and reduces the loss of antibacterial agents due to external factors; allowing antibacterial components to play a long-lasting role, avoiding the decay of antibacterial effect due to rapid consumption or loss of antibacterial agents, thereby ensuring the antibacterial durability of the coating. Attached Figure Description

[0022] Figure 1 This diagram illustrates the preparation method of the antibacterial coating for plywood according to the present invention. Figure 2 The figures show the hydrophobic test results of the antibacterial coatings in Examples 1-7 and Comparative Examples 9-11 of the present invention. Detailed Implementation

[0023] 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.

[0024] Please see Figures 1 to 2 This invention provides an antibacterial coating for plywood and its preparation method, the technical solution of which is as follows: Example 1 Preparation of polyurethane A solution: Under nitrogen protection, 5g of 1,4-butanediol was added to a 100mL three-necked flask, 27.8g of MDI was added, and 0.03g of DBTDL catalyst was added. The temperature was controlled at 80℃, and the mixture was stirred at 300rpm for 2h to obtain a prepolymer containing terminal NCO groups. 23.6 g of sodium 2,4-diaminobenzenesulfonate was pre-dissolved in 10 mL of LDMF to form a homogeneous sodium 2,4-diaminobenzenesulfonate solution. The prepolymer was cooled to 55 °C, and the sodium 2,4-diaminobenzenesulfonate solution was added to it. The mixture was stirred at 400 rpm for 1.5 h to form a chain-extended polyurethane. After the reaction, 5 mL of LDMF was added to dilute the viscosity. 23.6 g of isophorone diisocyanate was added, and the temperature was controlled at 70 °C. The mixture was stirred at 300 rpm for 1.5 h to obtain polyurethane solution A containing NCO terminal groups.

[0025] Preparation of perfluorooctyltriethoxysilane solution B: 2.83 g of perfluorooctyltriethoxysilane was added to a mixed solvent of 20 mL ethanol and 5 mL deionized water, and 50 μL of 0.1 mol / L hydrochloric acid solution was added as catalyst. The mixture was stirred at 200 rpm for 1 h at a temperature controlled at 25 °C to obtain hydrolyzed perfluorooctyltriethoxysilane solution B. After filtration, the solution was dried in an oven at 60 °C to obtain hydrolyzed perfluorooctyltriethoxysilane. This hydrolyzed perfluorooctyltriethoxysilane was then dissolved in 20 mL of LDM to obtain perfluorooctyltriethoxysilane solution B. Preparation of quaternary ammonium salt-supported nanoceramics: 1.7 g calcium nitrate and 1.8 g triethyl phosphate were added to 50 mL ethanol and stirred at 300 rpm for 30 min at 25 °C to form a homogeneous solution. Then, 10 mL deionized water and 50 μL 0.1 mol / L hydrochloric acid were added, and the mixture was stirred at 400 rpm for 2 h at 30 °C to carry out hydrolysis and condensation, forming a gel. The gel was dried at 80 °C for 4 h to form a dry gel. The temperature was then increased to 200 °C at a rate of 5 °C / min, held for 15 min, and then sintered at 500 °C. The heating rate was kept constant to obtain nano-calcium phosphate ceramics with a particle size of 50-100 nm. 0.5 g of nano-ceramics were dispersed in 10 mL of ethanol, and 0.3 g of dodecyl dimethyl ammonium chloride and 0.35 g of KH-550 were added. The mixture was stirred at 500 rpm for 1 h at 25 °C to allow dodecyl dimethyl ammonium chloride to be physically adsorbed onto the ceramic surface. KH-550 formed Si-OP or Si-O-Ca bonds by condensation with hydroxyl groups on the ceramic surface through silanol groups. After centrifugation, washing, and drying, modified quaternary ammonium salt supported nano-ceramics were obtained.

[0026] End-capping and cross-linking reaction: The obtained solution A was cooled to 40℃, and 2.50g of solution B was added dropwise over 30 minutes. The mixture was stirred at 300rpm for 1 hour, with the temperature controlled at 40℃, to allow some NCO groups to react with the silanol groups of perfluorooctyltriethoxysilane to form fluorosilicone-terminated polyurethane. Then, 0.5g of modified quaternary ammonium salt-supported nanoceramics was added, and the mixture was stirred at 400rpm for 30 minutes at 40℃, allowing the amino groups on the ceramic surface to react with the remaining NCO groups in solution A to form urea bonds, achieving chemical bonding between the ceramic and the polyurethane. Finally, 2.1g of KH-550 and 0.05g of scandium trifluoromethanesulfonate catalyst were added, and the temperature was raised to 50℃. The mixture was stirred at 300rpm for 30 minutes to ensure complete reaction of all NCO groups and unreacted silanol groups in solution B. Afterwards, unreacted substances, organic solvents, and catalysts were removed under reduced pressure.

[0027] Preparation of antibacterial coating: 0.2g of nano-silver, 0.5g of modified quaternary ammonium salt supported nano-ceramics, 0.2g of PVP and 0.1g of BYK-028 were added to the end-capped polyurethane and stirred at 1000rpm for 20min at 25℃; 0.05g of triethylamine and 21.29g of deionized water were added and stirred at 500rpm for 10min, and the viscosity was adjusted to 130mPa·s to obtain the antibacterial coating.

[0028] Examples 2-7 Unlike Example 1, the following preparation methods have been changed, as summarized in Tables 1 and 2. It should be noted that the modified quaternary ammonium salt-supported nanoceramics were added in two stages: once during the end-capping and cross-linking reaction, and the remaining stage during the preparation of the antibacterial coating, with each addition being half of the total amount.

[0029] Comparative Examples 1-12 are identical to Example 3 except for the following changes in preparation method, as detailed below.

[0030] Comparative Example 1 used 25.0 g of MDI and the prepolymerization temperature was 50 °C.

[0031] Comparative Example 2: The chain extender sodium 2,4-diaminobenzenesulfonate was replaced with an equal amount of 1,4-butanediol (10.0 g).

[0032] Comparative Example 3: Before the chain extension reaction, the prepolymer reacted directly without cooling.

[0033] In Comparative Example 4, 15g of isophorone diisocyanate was added, and the subsequent reaction temperature was 100℃.

[0034] In the preparation of quaternary ammonium salt-supported nanoceramics in Comparative Example 5, the preheating and holding process was not performed; instead, the temperature was directly increased to 500℃ at a heating rate of 5℃ / min for calcination.

[0035] In Comparative Example 6, the quaternary ammonium salt-supported nanoceramics were not added in two separate steps, but were added directly during the end-capping and cross-linking reaction.

[0036] Comparative Example 7: Nanoceramics without any quaternary ammonium salts added.

[0037] Comparative Example 8: The quaternary ammonium salt-supported nanoceramics were replaced with an equal mass of quaternary ammonium salt bis(dodecyl)dimethylammonium chloride, while other preparation methods remained unchanged.

[0038] Comparative Example 9: No solution B added.

[0039] Comparative Example 10: No KH-550 supplemental capping agent added.

[0040] In Comparative Example 11, during the end-capping and cross-linking reaction, after adding KH-550 and scandium trifluoromethanesulfonate catalyst, the temperature was raised to 100℃.

[0041] Comparative Example 12: Nano-ceramics without added nano-silver and modified quaternary ammonium salt.

[0042] Table 1. Preparation of polyurethane solution A, perfluorooctyltriethoxysilane solution B, and quaternary ammonium salt-supported nanoceramics Table 2. Preparation, end-capping and cross-linking reactions, and antibacterial coating preparation of quaternary ammonium salt-supported nanoceramics Experimental Example 1 The antibacterial coatings prepared in Examples 1-7, Comparative Examples 1-5, Comparative Examples 7, and Comparative Examples 9-11 were applied to plywood. The specific applications are as follows: The plywood surface was pretreated by sanding with 320-grit sandpaper to remove surface wax and impurities, and then cleaned with ethanol. A spraying process was used, with the spray gun pressure set to 0.3 MPa and the spraying distance 20 cm. The antibacterial coating was evenly sprayed onto the plywood surface, with a coating thickness controlled at 30-50 μm. Finally, it was placed in a 60°C oven for curing for 30 min, and then allowed to cure naturally at 25°C for 24 h to obtain a dry antibacterial coating.

[0043] The adhesion strength of the dried antibacterial coating was tested using the following method: Using a multi-bladed cutting tool with 1mm spacing, suitable for soft substrates such as plywood, six parallel cuts were made into the coating surface, penetrating into the substrate. Then, six more vertical cuts were made at a 90° angle, forming a rectangular grid pattern of 25 squares. Care was taken not to damage the substrate during cutting. Cleaning: A soft brush was used to gently brush five times along the diagonal of the grid to remove debris. Adhesive tape conforming to ISO 2409:1999 was applied to the grid area, pressing evenly with the fingers to ensure tight contact. After approximately 90 seconds, the tape was quickly and smoothly peeled off at a 60° angle. The coating peeling in the grid area was visually inspected according to ISO standards. The 2409 six-level classification standard (levels 0-5) scoring is as follows: Level 0: smooth cut edge, no peeling; Level 1: small peeling, affected area ≤5%; Level 2: peeling area 6-15%; Level 3: peeling area 16-35%; Level 4: peeling area 36-65%; Level 5: peeling area >65% or complete peeling; the test was conducted at 23℃ and 50% relative humidity, with at least 3 different areas tested for each sample, and the average value was taken; the final test results are shown in Table 3.

[0044] Table 3 Adhesion performance test results of antibacterial coating The antibacterial coating prepared according to the method of this invention exhibits good adhesion to plywood. Under the conditions of Examples 1-7, the adhesion level was 0. During the preparation of polyurethane A solution, the two hydroxyl groups of 1,4-butanediol in the prepolymerization reaction reacted with the isocyanate groups of MDI under DBTDL catalysis to generate a polyurethane prepolymer with NCO terminal groups, forming urethane bonds. The NCO / OH ratio was basically controlled at 2:1 to ensure that active NCO groups were retained at both ends of the prepolymer, providing reaction sites for subsequent chain extension and end-capping. The polyurethane prepolymer generated by the prepolymerization reaction endows the coating with good flexibility and mechanical strength, which helps the coating maintain its integrity when deformed on the plywood surface and reduces the risk of peeling. Excess NCO groups provide sufficient active sites for subsequent chain extension and end-capping reactions, ensuring chemical bonding with hydrolyzed perfluorooctyltriethoxysilane, KH-550 and nano-ceramics, enhancing the adhesion between the coating and the substrate. During the chain extension reaction, the amino group of sodium 2,4-diaminobenzenesulfonate reacted with the NCO terminal groups of the prepolymer to generate urea bonds, forming a high molecular weight chain-extended polyurethane.

[0045] The sulfonic acid groups of sodium 2,4-diaminobenzenesulfonate introduce hydrophilic properties, while DMF, as an aprotic solvent, prevents NCO from reacting with water, thus retaining active NCO. Urea bonds are more rigid than urethane bonds, increasing the mechanical strength of the coating and helping to resist peeling forces in severance tests. At the same time, the introduction of sulfonic acid groups also increases the adhesion between the coating and the wood board. The NCO groups of IPDI react with the residual amino groups of the chain-extended polyurethane to further extend the chain segments and retain the terminal NCO groups. The silanol groups of hydrolyzed perfluorooctyltriethoxysilane react with the terminal NCO groups for end-capping, while the free amino and hydroxyl groups contained in the modified ceramic react with NCO to form urea bonds, chemically bonding the ceramic to the polyurethane. The amino groups of KH-550 react with the remaining NCO and silanol groups to improve the degree of crosslinking. All these conditions work together to increase the adhesion of the coating to the plywood.

[0046] The coating adhesion in the comparative examples was lower than that in the examples. Under the conditions of Comparative Example 1, the reduction in MDI resulted in a lower molecular weight of the prepolymer, insufficient chain segment flexibility, and reduced coating toughness and adhesion. The prepolymerization temperature was too low, resulting in incomplete reaction between MDI and BDO. The residual -OH groups reduced the subsequent NCO reaction sites, affecting chain extension and end-capping, thus reducing adhesion. In Comparative Example 2, 1,4-butanediol was used instead. The sulfonic acid groups of sodium 2,4-diaminobenzenesulfonate provided hydrophilicity and hydrogen bonds with lignohydroxyl groups, while BDO only provided -OH groups, resulting in reduced hydrophilicity and surface affinity. The urethane bonds formed by 1,4-butanediol are more flexible than the urea bonds formed by sodium 2,4-diaminobenzenesulfonate, but their chemical bonding with the plywood surface is weaker. In Comparative Example 3, the prepolymer was not cooled before the chain extension reaction and reacted directly at 80℃. The aromatic amine reactivity of sodium 2,4-diaminobenzenesulfonate is low. At 80℃, NCO self-polymerization or weak coordination with DMF is initiated, resulting in uneven chain segments, reduced coating strength, and the lack of cooling destroys the stability of sodium 2,4-diaminobenzenesulfonate, reduces hydrophilicity, and affects the hydrogen bonding with the plywood. In Comparative Example 4, isoflavones... With reduced dosage of ketone diisocyanate and increased reaction temperature, excessive cross-linking of polyurethane segments led to decreased coating flexibility and easy peeling during cutting. Comparative Example 5, lacking a pre-calcination step, resulted in incomplete volatilization of organic residues in the gel. Sintering at 500℃ caused ceramic structural defects, reducing surface hydroxyl and amino groups, affecting subsequent end-capping and bonding. Unbonded nanoceramics were removed during subsequent decompression, and the final adhesion remained unaffected. Comparative Example 7, without adding any quaternary ammonium salt-loaded nanoceramics, showed no significant impact on adhesion performance. The fluorocarbon chains and silanol groups in Comparative Example 9 provided… The absence of hydrophobicity and end-capping properties increases the hydrophilicity of the coating, making it more susceptible to moisture. This reduces the number of chemical bonding points in the coating, significantly decreasing adhesion. In Comparative Example 10, the amino end-capping of KH-550 leaves residual NCO. The excess NCO reacts with ambient moisture, generating bubbles and causing coating defects. Simultaneously, the degree of crosslinking decreases, reducing coating stability. In Comparative Example 11, the end-capping and crosslinking reaction temperature is too high. The hydroxyl groups of the sulfonic acid group crosslink with the amino groups of KH-550, affecting the end-capping of the silanol groups present in the system, thus reducing adhesion.

[0047] Experimental Example 2 The antibacterial coatings prepared in Examples 1-7 and Comparative Examples 9-11 were applied to plywood. The specific application method was the same as in Experimental Example 1. After complete drying and curing, a waterproof performance test was conducted. The specific test method was as follows: The sample was placed on the horizontal platform of a contact angle measuring instrument and adjusted to a horizontal state; using a micro-syringe with a needle inner diameter of 0.5 mm, 2-5 µL of deionized water was dropped onto the coating surface; the contact angle image between the water droplet and the coating surface was immediately captured by a camera within 1-5 seconds after droplet application to avoid the influence of evaporation. A static contact angle measurement method was used, and the contact angle between the water droplet and the surface was calculated using the instrument software. At least three different locations were tested for each sample, and the average value was taken. The final test results are shown in Table 4 and... Figure 2 As shown.

[0048] Table 4. Waterproofing performance test results of antibacterial coating The antibacterial coating prepared according to the method of the present invention, when used on plywood, exhibits good hydrophobic properties. Specific hydrophobic values ​​are shown in Table 4. Figure 2 The hydrophobic angles of the coatings prepared by the comparative examples under the conditions shown in Examples 1-7 are all >100°, indicating a decrease in the hydrophobic effect of the coatings obtained by the comparative examples. The comparative examples did not add perfluorooctyltriethoxysilane B solution, which is responsible for consuming some NCO during end-capping. The absence of NCO leads to the reaction of NCO with moisture to generate carbon dioxide, causing bubble defects in the coating and reducing its density. Furthermore, the lack of silicon and fluorine further hinders the formation of good hydrophobicity, resulting in a decrease in hydrophobic performance. Comparative Example 10 did not add KH-550 to supplement the end-capping agent, reducing chemical bonding points and resulting in a loose coating network that allows for easy water penetration. The coupling agent simultaneously acts as a crosslinking and self-hydrophobic agent, and its absence further reduces the hydrophobic effect. Comparative Example 11, with its high-temperature initiation of crosslinking between the sulfonic acid groups of sodium 2,4-diaminobenzenesulfonate and the amino groups of KH-550, interferes with the end-capping of silanol groups, reducing chemical bonding with the plywood. While the overall hydrophobic effect is lower than the examples, it is still better than the results of Comparative Examples 1 and 2.

[0049] Experimental Example 3 The antibacterial coatings prepared in Examples 1-7 and Comparative Examples 5-12 were applied to plywood. The specific application method was the same as in Experimental Example 1. After complete drying and curing, the antibacterial performance was tested. The specific testing method was as follows: ATCC 8739 *Escherichia coli* was selected for testing. The strain was cultured to the logarithmic growth phase, and the bacterial concentration was adjusted to approximately 2.5 × 10⁻⁶. 5CFU / mL, add 0.4 mL of bacterial solution to the surface of each test piece, cover evenly, and then cover with a 40 mm × 40 mm polyethylene film to ensure full contact between the bacterial solution and the coating. Place the test piece in a petri dish and incubate at 35±1℃ and relative humidity ≥90% for 24 hours. After incubation, rinse the test piece and film with 10 mL of soybean casein lecithin Tween medium, recover the bacteria, release the recovered solution, spread it on nutrient agar plates, and incubate at 35℃ for 48 hours. Count the surviving colonies (CFU / mL). The antibacterial rate is calculated as follows: Antibacterial rate (%) = (Number of surviving bacteria in the control group - Number of surviving bacteria in the test sample) / Mean number of surviving bacteria in the control group × 100%; where the control group is the plywood group without antibacterial coating; repeat the experiment three times and calculate the average value. The antimicrobial durability of the fully cured antimicrobial coating was tested. The specific test method is as follows: The test piece was placed in deionized water at 25°C and washed with a standard washing device (simulating ASTM D896) at 100 rpm for 5 minutes each time, for a total of 100 times, with fresh deionized water replaced each time; after washing, the test piece was dried in an oven at 50°C for 30 minutes and then allowed to return to room temperature. The antimicrobial rate of the test piece after washing was tested according to ISO 22196 method, with the same steps as above (bacterial strain, inoculation, culture, bacterial recovery, and counting). The antimicrobial rate after washing was calculated and compared with the initial antimicrobial rate. The final test results are shown in Table 5.

[0050] Table 5 Results of antibacterial properties and antibacterial durability tests The antibacterial coating prepared according to the method of this invention exhibits good antibacterial properties and antibacterial durability under the conditions described in the examples. Excellent antibacterial properties and antibacterial durability are achieved through the antibacterial properties of nano-silver, the long-term release of quaternary ammonium salts from quaternary ammonium salt-loaded nano-ceramics, and end-capping with hydrolyzed perfluorooctyltriethoxysilane and chemical cross-linking. The principle of the cross-linking reaction during the preparation process is shown in the results analysis below Example 1. Cross-linking increases the density of the coating, preventing water and *E. coli* from penetrating into the plywood through the coating, thus improving antibacterial properties. Deionized water and hydrochloric acid solution are added to calcium nitrate and triethyl phosphate ethanol and stirred to form a gel. Subsequent calcination yields nano-calcium phosphate bioceramics. The high specific surface area of ​​these nano-calcium phosphate bioceramics provides numerous attachment sites for quaternary ammonium salts. Upon slow release, the positively charged quaternary ammonium salts adsorb the negatively charged cell walls of *E. coli*, disrupting the membrane structure and causing leakage of cell contents. The slow release of silver ions from nano-silver damages the cell membrane and DNA, inhibiting the growth of *E. coli*, thus achieving long-lasting antibacterial properties.

[0051] In Comparative Example 6, the quaternary ammonium salt-supported nanoceramics were added directly during the end-capping and cross-linking reaction, rather than in two separate additions. The initial antibacterial activity was comparable to Example 3, but the organic residue from ceramic defects reduced the fixation of di-dodecyl dimethyl ammonium chloride and KH-550, leading to a decrease in antibacterial rate after washing. Comparative Example 7, lacking nanoceramics, relied on nano-silver for antibacterial activity; silver ions were lost after washing, resulting in poor durability. In Comparative Example 8, di-dodecyl dimethyl ammonium chloride was added directly without a ceramic support; the physical adsorption of di-dodecyl dimethyl ammonium chloride was unstable, resulting in a low initial antibacterial rate, significant loss after washing, and decreased antibacterial durability. Example 9: Initial antibacterial properties were maintained by nano-silver and bis(dodecyl)dimethylammonium chloride, but without hydrophobic protection from hydrolyzed perfluorooctyltriethoxysilane, the antibacterial durability decreased after repeated washing. Comparative Example 10: Initial antibacterial properties were supported by nano-silver and bis(dodecyl)dimethylammonium chloride, but without KH-550 crosslinking, the antibacterial agent was poorly fixed, resulting in poor antibacterial durability. Comparative Example 11: The temperature during the end-capping and crosslinking reactions was too high, slightly reducing the fixation effect of the antibacterial agent, and the antibacterial durability decreased. Comparative Example 12: Without nano-silver and nano-ceramics, containing only a polyurethane matrix without antibacterial agent, the antibacterial properties and durability decreased significantly.

[0052] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an antibacterial coating for plywood, characterized in that: The preparation method is as follows: After cooling polyurethane liquid A, perfluorooctyltriethoxysilane liquid B is added dropwise to polyurethane liquid A to form fluorinated silicone polyurethane. Modified nano-ceramic supported quaternary ammonium salt is added to the fluorinated silicone polyurethane, and the reaction is stirred. Finally, coupling agent γ-aminopropyltriethoxysilane and catalyst are added, the temperature is raised to 50°C, and the reaction is carried out under reduced pressure to obtain end-capped polyurethane. Nano-silver, the modified nano-ceramic supported quaternary ammonium salt, polyvinylpyrrolidone, and defoamer are added to the end-capped polyurethane, and the viscosity is adjusted after stirring to obtain the antibacterial coating for plywood. The polyurethane A liquid was obtained through a prepolymerization reaction and a chain extension reaction. Specifically, under nitrogen protection, 5g of 1,4-butanediol was added to a 100mL three-necked flask, along with 27.8g of 4,4'-methylenebis(phenyl isocyanate) and 0.03g of dibutyltin dilaurate catalyst. The temperature was controlled at 80℃, and the mixture was stirred at 300rpm for 2 hours to obtain a prepolymer containing NCO terminal groups. 23.6 g of sodium 2,4-diaminobenzenesulfonate was dissolved in 10 mL of N,N-dimethylformamide to form a homopolymer sodium 2,4-diaminobenzenesulfonate solution. The prepolymer was cooled to 55 °C, and the sodium 2,4-diaminobenzenesulfonate solution was added to it. The mixture was stirred at 400 rpm for 1.5 h to form a chain-extended polyurethane. After the reaction, 5 mL of N,N-dimethylformamide was added to dilute the viscosity. 23.6 g of isophorone diisocyanate was added, and the temperature was controlled at 70 °C. The mixture was stirred at 300 rpm for 1.5 h to obtain the polyurethane solution A containing NCO terminal groups. The modified nano-ceramic loaded with quaternary ammonium salt is obtained by preparing nano-calcium phosphate ceramics by sol-gel method and then loading quaternary ammonium salts; the process of loading quaternary ammonium salts is as follows: the nano-calcium phosphate ceramics are dispersed in ethanol, and bis(dodecyl)dimethylammonium chloride and γ-aminopropyltriethoxysilane are added. After stirring at room temperature, the mixture is centrifuged, washed, and dried. The sol-gel method is as follows: calcium nitrate and triethyl phosphate are added to ethanol to form a homogeneous solution; hydrochloric acid is added to the homogeneous solution to hydrolyze and condense to obtain a gel, which is then dried to obtain a dry gel; the dry gel is calcined after being subjected to programmed temperature increases to obtain the nano-calcium phosphate ceramic. The programmed temperature rise conditions are as follows: starting from 80°C, the temperature is increased to 150-220°C at a rate of 5°C / min, held for 15-40 minutes, and then increased to 450-600°C for sintering for 1 hour.

2. The method for preparing an antibacterial coating for plywood according to claim 1, characterized in that, The preparation method of the perfluorooctyltriethoxysilane B solution is as follows: perfluorooctyltriethoxysilane is added to ethanol and deionized water, and hydrochloric acid is added to carry out hydrolysis reaction. After the reaction is completed, the solution is filtered, dried, and redissolved to obtain the perfluorooctyltriethoxysilane B solution.

3. An antibacterial coating for plywood, characterized in that: The antibacterial coating is prepared by the preparation method according to any one of claims 1-2; the viscosity of the antibacterial coating is 100-150 mPa·s; the method of using the antibacterial coating on the plywood is as follows: the surface of the plywood is pretreated by sanding with sandpaper to remove surface wax and impurities, and then wiped clean with ethanol; the antibacterial coating is uniformly sprayed onto the surface of the plywood using a spraying process, and the coating thickness is controlled at 30-50 μm; finally, it is placed in a 60℃ oven for curing for 30 min, and then allowed to cure naturally at room temperature to obtain a dry antibacterial coating.

Images