Antibacterial coating for plywood and preparation method thereof

Abstract

The invention relates to the technical field of antibacterial coatings, in particular to an antibacterial coating for plywood and a preparation method of the antibacterial coating. The problems that the adhesive force between the antibacterial coating and the plywood is poor, and the antibacterial durability is poor are solved; the preparation method comprises the following steps: carrying out a pre-polymerization reaction and a chain extension reaction to obtain a polyurethane solution, carrying out end capping treatment by using a hydrolyzed fluorine-containing silane solution, loading quaternary ammonium salt on nano-ceramics, connecting the nano-ceramics with polyurethane through chemical bonds, and finally carrying out crosslinking by using a coupling agent to obtain the antibacterial coating. By adjusting the raw materials and the preparation method, the coating and the plywood have good adhesiveness; and the nano ceramic has a slow release effect on the antibacterial quaternary ammonium salt and has a lasting antibacterial effect together with the nano silver, so that the antibacterial effect is still good even after repeated washing.

Description

Technical Field

[0001] The present invention relates to the technical field of antibacterial coatings, in particular to an antibacterial coating for plywood and a preparation method thereof. Background Art

[0002] Plywood, a man-made board made of multiple layers of thin wood veneer glued together, is widely used in furniture, construction, packaging and other fields due to its high strength, good stability and easy processing. However, in environments with high humidity or high hygiene requirements, plywood is prone to breeding bacteria and fungi, which limits its scope of application. Therefore, the development of antibacterial coatings has become an important research direction to improve the functionality of plywood. In the existing technology, the antibacterial coating on the surface of plywood is mainly based on organic polymers or inorganic materials such as nano-titanium dioxide, and antibacterial agents are added to achieve antibacterial effects. Common preparation methods include spraying, dipping, chemical grafting and UV curing.

[0003] In existing technologies, polyurethane coatings are widely used due to their excellent adhesion and wear resistance, but traditional solvent-based polyurethanes have the problem of high volatile organic compound emissions. Water-based polyurethanes are gradually gaining attention as environmentally friendly alternatives, but their durability and antibacterial effects still need to be optimized. Nanosilver has been widely studied for its broad-spectrum antibacterial properties and is embedded in coatings through physical doping or chemical grafting, but it is easily lost over time, resulting in insufficient antibacterial durability. Although photocatalytic antibacterial agents have self-cleaning properties, they require ultraviolet light irradiation, which limits their indoor application. Natural antibacterial agents such as chitosan are environmentally friendly but have weak antibacterial effects and cannot meet high standards.

[0004] In addition, silicone-based coatings, as an emerging antimicrobial coating matrix, have attracted attention due to their excellent weather resistance, hydrophobicity, and chemical stability. By forming a flexible, durable coating, silicone can enhance the fixation effect of the antimicrobial agent and improve the antifouling properties of the coating. However, the adhesion of silicone coatings to plywood surfaces is poor and needs to be improved through surface modification or the addition of coupling agents. In addition, the hydrophobicity of silicone coatings may affect the uniform dispersion of the antimicrobial agent, resulting in unstable antimicrobial effects. Existing technologies generally have the problem of poor adhesion between the coating and the plywood substrate, especially on rough or waxy plywood surfaces. The coating is prone to peeling, affecting its service life. At the same time, insufficient antimicrobial durability remains a key issue. The antimicrobial agent is easily lost due to friction or water washing, limiting the long-term application effect of the coating.

[0005] In view of the shortcomings of existing technologies, there is an urgent need to develop an antibacterial coating based on water-based polyurethane and combining the advantages of silicone. By optimizing the antibacterial agent 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 protection and low cost.

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

[0007] The present invention provides an antibacterial coating for plywood and a method for preparing the same. A polyurethane solution is obtained through a prepolymerization reaction and a chain extension reaction, which is then capped using a hydrolyzed fluorinated silane solution. A quaternary ammonium salt is then loaded onto a nanoceramic, which is then chemically bonded to the polyurethane. Finally, a coupling agent is used for cross-linking to obtain the antibacterial coating. Adjustments to the raw materials and preparation method ensure that the coating has good adhesion to the plywood. Furthermore, the nanoceramic has a sustained-release effect on the antibacterial quaternary ammonium salt, which, together with nanosilver, produces a long-lasting antibacterial effect that remains effective even after repeated washings.

[0008] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing an antibacterial coating for plywood, and the preparation method is as follows: After the polyurethane liquid A is cooled, perfluorooctyltriethoxysilane liquid B is added dropwise to the polyurethane liquid A to react and form a fluorosilicone-terminated polyurethane; modified quaternary ammonium salt-loaded nanoceramics are added to the fluorosilicone-terminated polyurethane, stirred for reaction, and finally a coupling agent and a catalyst are added, the temperature is raised, the reaction is carried out, and the pressure is reduced to obtain the terminated polyurethane; Nanosilver, modified quaternary ammonium salt-loaded nanoceramics, polyvinyl pyrrolidone, and a defoaming agent are added to blocked polyurethane, and deionized water is added. After stirring, the viscosity is adjusted to obtain an antibacterial coating for plywood. The addition of deionized water increases the viscosity of the antibacterial coating to 100-150 mPa·s. The nanoceramics are added in batches to reduce agglomeration, ensure uniform distribution of the quaternary ammonium salt and nanosilver, and allow the reaction to proceed completely.

[0009] Polyurethane A liquid is obtained through prepolymerization and chain extension reaction; The modified quaternary ammonium salt loaded nano ceramics are prepared by a sol-gel method to obtain nano calcium phosphate ceramics and then loaded with quaternary ammonium salt.

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

[0011] Preferably, the chain extension reaction process is as follows: cooling the prepolymer obtained by the prepolymerization reaction, adding a sodium 2,4-diaminobenzenesulfonate solution and stirring for reaction, adding N,N-dimethylformamide for viscosity dilution, adding isophorone diisocyanate, and heating for reaction.

[0012] Preferably, the preparation method of perfluorooctyltriethoxysilane liquid B 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 mixture is filtered, dried, and redissolved to obtain perfluorooctyltriethoxysilane liquid B.

[0013] Preferably, the sol-gel method is as follows: calcium nitrate and triethyl phosphate are added to ethanol to form a uniform solution; hydrochloric acid is added to the uniform solution for hydrolysis and polycondensation to obtain a gel, and the gel is dried to obtain a dry gel; the dry gel is subjected to programmed temperature and then calcined to obtain nano calcium phosphate ceramics.

[0014] Preferably, the programmed temperature is as follows: starting from 80° C., heating to 150-220° C. at a heating rate of 5° C. / min, maintaining for 15-40 min, then heating to 450-600° C. and sintering for 1 h.

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

[0016] The present 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-loaded nanoceramics. The viscosity of the antibacterial coating is 100-150 mPa·s. The antibacterial coating is used on the plywood as follows: pre-treating the surface of the plywood, polishing with sandpaper to remove surface wax and impurities, and wiping with ethanol to clean it; using a spraying process to evenly spray the antibacterial coating on the surface of the plywood, with the coating thickness controlled to be 30-50 μm; and finally curing in a 60°C oven for 30 minutes, and naturally curing at room temperature to obtain a dry antibacterial coating.

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

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. By regulating each reaction step in the polyurethane preparation process, the adhesion of the antimicrobial coating to plywood is significantly improved. The prepolymerization stage controls the reaction ratio and conditions to produce a prepolymer containing active NCO groups at both ends, providing ample sites for subsequent reactions while imparting the coating with appropriate flexibility and mechanical strength. The chain extension stage introduces specific groups to enhance the coating's mechanical strength and improve its affinity with the plywood surface. The end-capping and cross-linking processes increase the degree of cross-linking through the synergistic reaction of multiple components, achieving chemical bonding between the coating and the substrate. This ensures the coating's stable adhesion to the plywood surface and resists peeling even if the substrate deforms, fundamentally guaranteeing the coating's adhesion to the plywood.

[0019] 2. The prepared antibacterial coating has a good hydrophobic effect on plywood. The hydrolyzed perfluorooctyltriethoxysilane participates in the end-capping reaction, and the silicon and fluorine elements it contains 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, it reduces the adhesion and penetration of water on the coating surface. Reasonable adjustment of the preparation method also enables the effective combination of hydrophobic-related components, thereby stably maintaining the hydrophobic effect of the coating.

[0020] 3. The introduction of nanosilver releases silver ions that inhibit bacterial growth; the addition of quaternary ammonium salt-loaded nanoceramics, and the slow-released quaternary ammonium salt contributes to the antibacterial persistence; at the same time, the cross-linking reaction increases the density of the coating, forming a physical barrier to prevent bacteria from penetrating into the plywood; the synergistic effect of chemical sterilization and physical barrier effectively improves the antibacterial performance of the coating.

[0021] 4. Ensure the coating's long-lasting antibacterial properties through reasonable design; nanoceramics provide attachment sites for quaternary ammonium salts with a high specific surface area, enabling their slow release; nanosilver can also continuously release silver ions to maintain bactericidal ability; cross-linking reactions enhance the stability of the coating structure and reduce the loss of antibacterial agents due to external factors; allowing the antibacterial ingredients to exert their effects for a long time, avoiding the attenuation of the antibacterial effect due to rapid consumption or loss of antibacterial agents, thereby ensuring the coating's long-lasting antibacterial properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A diagram showing a method for preparing an antibacterial coating for plywood according to the present invention; Figure 2 Graph showing the hydrophobicity test results of the antibacterial coatings of Examples 1-7 and Comparative Examples 9-11 of the present invention. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] See also Figures 1 to 2 The present invention provides an antibacterial coating for plywood and a preparation method thereof. The technical solution is as follows: Example 1 Preparation of polyurethane liquid A: Under nitrogen protection, add 5g of 1,4-butanediol into a 100mL three-necked flask, add 27.8g of MDI, add 0.03g of DBTDL catalyst, control the temperature at 80℃, and stir 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 DMF to form a sodium 2,4-diaminobenzenesulfonate solution; the prepolymer was cooled to 55° C., the sodium 2,4-diaminobenzenesulfonate solution was added thereto, and the mixture was stirred at 400 rpm for 1.5 hours to form a chain-extended polyurethane. After the reaction, 5 mL of DMF was added for viscosity dilution; 23.6 g of isophorone diisocyanate was added, the temperature was controlled at 70° C., and the mixture was stirred at 300 rpm for 1.5 hours to obtain a polyurethane A liquid containing terminal NCO groups.

[0025] Preparation of perfluorooctyltriethoxysilane solution B: 2.83 g of perfluorooctyltriethoxysilane was added to a mixed solvent of 20 mL of ethanol and 5 mL of deionized water, 50 μL of a 0.1 mol / L hydrochloric acid solution as a catalyst was added, and the mixture was stirred at 200 rpm for 1 hour at a temperature of 25°C to obtain hydrolyzed perfluorooctyltriethoxysilane solution B. The mixture was filtered and dried in an oven at 60°C to obtain hydrolyzed perfluorooctyltriethoxysilane, which was then dissolved in 20 mL of DMF to obtain perfluorooctyltriethoxysilane solution B. Preparation of quaternary ammonium salt-loaded nanoceramics: 1.7 g of calcium nitrate and 1.8 g of triethyl phosphate were added to 50 mL of ethanol and stirred at 300 rpm for 30 min at 25 °C to form a uniform solution; 10 mL of deionized water and 50 μL of 0.1 mol / L hydrochloric acid were then added and stirred at 400 rpm for 2 h. The temperature was controlled at 30 °C for hydrolysis and polycondensation to form a gel; the gel was dried at 80 °C for 4 h to form a dry gel, and the temperature was raised to 200 °C at a rate of 5 °C / min, maintained for 15 min, and then raised to 500 °C for sintering. h, the heating rate remains unchanged to obtain nano calcium phosphate ceramics with a particle size of 50-100 nm; 0.5 g of nano ceramics is dispersed in 10 mL of ethanol, 0.3 g of didodecyl dimethyl ammonium chloride and 0.35 g of KH-550 are added, and the mixture is stirred at 500 rpm for 1 h at a temperature of 25°C to allow didodecyl dimethyl ammonium chloride to be loaded on the ceramic surface by physical adsorption, and KH-550 is condensed with the hydroxyl groups on the ceramic surface through the silanol group to form Si-OP or Si-O-Ca bonds, and the mixture is centrifuged, washed, and dried to obtain modified quaternary ammonium salt-loaded nano ceramics.

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

[0027] Preparation of antibacterial coating: 0.2 g of nanosilver, 0.5 g of modified quaternary ammonium salt-loaded nanoceramic, 0.2 g of PVP, and 0.1 g of BYK-028 were added to the blocked polyurethane and stirred at 1000 rpm for 20 min at 25°C. 0.05 g of triethylamine and 21.29 g of deionized water were added and stirred at 500 rpm for 10 min. The viscosity was adjusted to 130 mPa·s to obtain the antibacterial coating.

[0028] Examples 2-7 The difference from Example 1 is that the following preparation method is changed, which is specifically summarized in Tables 1 and 2. It should be noted that the modified quaternary ammonium salt-loaded nanoceramics are added twice, once during the end-capping and cross-linking reaction process, and the remaining amount is added during the preparation of the antibacterial coating, and the amount added each time is half of the total amount.

[0029] Comparative Examples 1-12 Except for the following changes in the preparation method, the others are consistent with Example 3, as shown below.

[0030] Comparative Example 1 The amount of MDI used was 25.0 g, and the temperature of the prepolymerization reaction 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 was directly reacted without cooling.

[0033] Comparative Example 4 The amount of isophorone diisocyanate added was 15 g, and the subsequent reaction temperature was 100°C.

[0034] Comparative Example 5 During the preparation of the quaternary ammonium salt-loaded nanoceramics, the preheating and heat preservation process was omitted, but the temperature was directly raised to 500° C. at a heating rate of 5° C. / min for calcination.

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

[0036] Comparative Example 7 No quaternary ammonium salt was added to support the nanoceramics.

[0037] Comparative Example 8 The quaternary ammonium salt-loaded nanoceramics were replaced with an equal mass of quaternary ammonium salt didodecyldimethylammonium chloride, and the other preparation methods remained unchanged.

[0038] Comparative Example 9: Liquid B was not added.

[0039] Comparative Example 10: No KH-550 supplementary end-capping agent was added.

[0040] 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°C.

[0041] Comparative Example 12: No nanosilver and modified quaternary ammonium salt-loaded nanoceramics were added.

[0042] Table 1 Preparation of polyurethane solution A, perfluorooctyltriethoxysilane solution B, and quaternary ammonium salt-loaded nanoceramics Table 2 Preparation, end-capping and cross-linking reactions of quaternary ammonium salt-loaded nanoceramics, and preparation of antibacterial coatings Experimental Example 1 The antibacterial coatings prepared in Examples 1-7, Comparative Examples 1-5, Comparative Example 7, and Comparative Examples 9-11 were applied to plywood. The specific application was as follows: the plywood surface was pretreated by polishing with 320-grit sandpaper to remove surface wax and impurities, and then wiping with ethanol to clean it. The antibacterial coating was evenly sprayed on the plywood surface using a spray gun pressure of 0.3 MPa and a spray distance of 20 cm. The coating thickness was controlled to be 30-50 μm. Finally, the plywood was placed in an oven at 60°C for curing for 30 minutes, followed by natural curing at 25°C for 24 hours to obtain a dry antibacterial coating.

[0043] The dry antimicrobial coating was tested for adhesion strength using the following method: using a multi-blade cutting tool with a 1mm spacing, suitable for soft substrates such as plywood, cut six parallel cuts deep into the substrate on the coating surface, followed by six perpendicular cuts at a 90° angle to form a rectangular grid pattern of 25 squares; ensuring that the substrate is not damaged during cutting; cleaning: using a soft brush to gently brush along the diagonal direction of the grid five times to remove shavings; applying adhesive tape that complies with ISO 2409:1999 standard to the grid area, pressing evenly with your fingers to ensure close contact, waiting for about 90 seconds, and then quickly and smoothly tearing off the tape at a 60° angle; visually inspecting the coating peeling condition in the grid area, according to ISO The 2409 was scored using a six-level classification standard (0-5): Level 0: smooth incision 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. Tests were conducted at 23°C and 50% relative humidity. Each sample was tested in at least three different areas 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 obtained by the preparation method of the present invention has excellent adhesion to plywood. Under the conditions of Examples 1-7, the adhesion grade is all grade 0. During the preparation of polyurethane liquid A, the two hydroxyl groups of 1,4-butanediol react with the isocyanate groups of MDI under the catalysis of DBTDL in the prepolymerization reaction to generate a polyurethane prepolymer with terminal NCO groups, forming a urethane bond. The NCO / OH ratio is basically controlled at 2:1, ensuring that active NCO groups are 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 imparts good flexibility and mechanical strength to the coating, helping the coating maintain its integrity when the plywood surface is deformed and reducing the risk of peeling. The excess NCO groups provide sufficient active sites for subsequent chain extension and end capping reactions, ensuring chemical bonding with hydrolyzed perfluorooctyltriethoxysilane, KH-550, and nanoceramics, thereby enhancing the bonding strength between the coating and the substrate. During the chain extension reaction, the amino groups of sodium 2,4-diaminobenzenesulfonate react with the NCO groups at the end of the prepolymer to form urea bonds, forming a high molecular weight chain-extended polyurethane.

[0045] The sulfonic acid group of sodium 2,4-diaminobenzenesulfonate introduces hydrophilic properties, and DMF acts as an aprotic solvent to prevent NCO from reacting with water, retaining active NCO; urea bonds are more rigid than carbamate bonds, increasing the mechanical strength of the coating and helping to resist peeling force in cross-cut tests. At the same time, the introduction of sulfonic acid groups also increases the adhesion of the coating to the wood board; the NCO group of IPDI reacts with the residual amino group of the extended polyurethane to further extend the chain segment and retain the terminal NCO group; the silanol group of hydrolyzed perfluorooctyltriethoxysilane reacts with the terminal NCO group for capping, and at the same time, 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 group of KH-550 reacts with the remaining NCO and silanol groups to increase the degree of cross-linking; the above conditions work together to increase the adhesion of the coating to the plywood.

[0046] The coating adhesion of the comparative example is lower than that of the embodiment. Under the conditions of comparative example 1, the reduction of MDI leads to a low molecular weight of the prepolymer, insufficient flexibility of the chain segments, and reduced toughness and adhesion of the coating. The prepolymerization temperature is too low, the reaction between MDI and BDO is incomplete, and the residual -OH group reduces the subsequent NCO reaction site, affecting chain extension and end capping, and the adhesion ability is reduced. Comparative example 2 is replaced with 1,4-butanediol. The sulfonic acid group of sodium 2,4-diaminobenzenesulfonate provides hydrophilicity and hydrogen bonds with wood hydroxyl groups, while BDO only provides -OH groups, and the hydrophilicity and surface affinity are reduced. The urethane bond formed by 1,4-butanediol is more flexible than the urea bond formed by sodium 2,4-diaminobenzenesulfonate, but its chemical bonding force with the plywood surface is weaker; in comparative example 3, the prepolymer is not cooled before the chain extension reaction, and the reaction is directly carried out at 80°C. The reactivity of the aromatic amine of sodium 2,4-diaminobenzenesulfonate is low, and 80°C triggers NCO self-polymerization or weak coordination with DMF, resulting in uneven chain segments and reduced coating strength. In addition, if the temperature is not lowered, the stability of sodium 2,4-diaminobenzenesulfonate is destroyed, the hydrophilicity is reduced, and the hydrogen bonding with the plywood is affected; in comparative example 4, the isoflurane isocyanate isocyanate isocyanate, and the hydrophilicity is reduced. The amount of phenol diisocyanate used is reduced, and the reaction temperature is increased, the polyurethane segments are over-crosslinked, the coating flexibility is reduced, and it is easy to peel off during cutting; Comparative Example 5 has no pre-calcination step, the organic residue in the gel is not completely volatilized, sintering at 500 ° C leads to ceramic structural defects, the surface hydroxyl and amino groups are reduced, affecting the subsequent end-capping and bonding, and the unbonded nanoceramics are removed in the subsequent decompression process, and the final adhesion is not affected; Comparative Example 7 does not add any quaternary ammonium salt to load the nanoceramics, and has no obvious effect on the adhesion performance; Comparative Example 9 has fluorocarbon chains and silicone hydroxyl groups. The hydrophobicity and end-capping effect increase the hydrophilicity of the coating after its loss, making it susceptible to moisture, reducing the chemical bonding points of the coating and significantly reducing the adhesion performance. In comparative example 10, the amino end-capping of KH-550 has residual NCO. After its loss, the excess NCO reacts with environmental moisture to generate bubbles, resulting in coating defects. At the same time, the degree of cross-linking decreases, and the coating stability decreases. In comparative example 11, the end-capping and cross-linking reaction temperature is too high, wherein the hydroxyl group of the sulfonic acid group cross-links with the amino group of KH-550, affecting the end-capping with the silicone hydroxyl group present in the system, and the adhesion ability is reduced.

[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 as described in Experimental Example 1. After complete drying and curing, a waterproof performance test was performed. 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; 2-5 μL of deionized water was dripped onto the coating surface using a micro-injector with a needle having an inner diameter of 0.5 mm; the contact angle image of the water droplet and the coating surface was immediately captured by a camera, and the image was measured within 1-5 seconds after the droplet was added to avoid the influence of evaporation. The static contact angle measurement method was used to calculate the contact angle between the water droplet and the surface using the instrument software. At least 3 different positions of each sample were tested, and the average value was taken; the final test results are shown in Tables 4 and 5. Figure 2 shown.

[0048] Table 4 Waterproof performance test results of antibacterial coating The antibacterial coating prepared according to the preparation method of the present invention has a good hydrophobic effect when used on plywood. The specific hydrophobicity values ​​are shown in Table 4. Figure 2 It shows that the hydrophobic angle under the conditions of Examples 1-7 is greater than 100°, and the hydrophobic effect of the coating obtained by the preparation method of the comparative example is reduced. Among them, the comparative example does not add perfluorooctyl triethoxysilane B liquid, which acts to consume part of the NCO by end-capping. After the loss, NCO reacts with water to generate carbon dioxide, causing bubble defects in the coating, reducing the compactness, and the lack of silicon and fluorine, which cannot play a good hydrophobic role, so the hydrophobic performance is reduced; Comparative Example 10 does not add KH-550 to supplement the end-capping agent, the chemical bonding points are reduced, the coating network is loose, and water is easily permeable. The coupling agent plays the role of cross-linking and self-hydrophobicity at the same time, and the absence of the coupling agent reduces the hydrophobic effect; Comparative Example 11 high temperature triggers the sulfonic acid group of sodium 2,4-diaminobenzenesulfonate to cross-link with the KH-550 amino group, interfering with the silanol end-capping, reducing the chemical bonding with the plywood, and the overall hydrophobic effect is reduced compared with the embodiment, but is better than the results of Comparative Example 1 and Comparative Example 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 as described in Experimental Example 1. After complete drying and curing, the antibacterial performance test was performed. The specific test method was as follows: Escherichia coli ATCC 8739 was selected for testing. The strain was cultured to the logarithmic growth phase, and the bacterial solution concentration was adjusted to about 2.5×10 5CFU / mL, 0.4 mL of bacterial solution was dripped onto the surface of each test piece, evenly covered, and then covered with a 40 mm × 40 mm polyethylene film to ensure full contact between the bacterial solution and the coating. The test piece was placed in a culture dish and incubated at 35 ± 1 ° C and relative humidity ≥ 90% for 24 hours. After incubation, the test piece and film were rinsed with 10 mL of soybean casein lecithin Tween medium, the bacteria were recovered, the recovered solution was released, and the plate was spread on a nutrient agar plate and incubated at 35 ° C for 48 hours. The surviving colonies (CFU / mL) were counted. The antibacterial rate was 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; the experiment was repeated three times, and the average value was calculated; The fully cured antibacterial coating was subjected to an antibacterial durability test. The specific test method was as follows: the test piece was placed in 25°C deionized water and washed with a standard washing device (simulating ASTM D896) at 100 rpm for 5 minutes each time, for a total of 100 times, and fresh deionized water was replaced each time; after washing, the test piece was dried in a 50°C oven for 30 minutes and returned to room temperature. The antibacterial rate of the cleaned test piece was tested according to the ISO 22196 method, with the same steps as above (bacterial species, inoculation, culture, bacterial recovery, and counting). The antibacterial rate after cleaning was calculated and compared with the initial antibacterial rate. The final test results are shown in Table 5.

[0050] Table 5 Antibacterial and antibacterial persistence test results The antibacterial coating prepared according to the preparation method of the present invention has excellent antibacterial properties and antibacterial persistence. The antibacterial properties are achieved through the antibacterial properties of nanosilver, the long-term release of quaternary ammonium salts in quaternary ammonium salt-loaded nanoceramics, and hydrolysis of perfluorooctyltriethoxysilane end-capping and chemical crosslinking, achieving excellent antibacterial properties and antibacterial persistence. The principle of the crosslinking reaction during the preparation process is shown in the results analysis below Experimental Example 1. Crosslinking increases the density of the coating, preventing water and E. coli from penetrating into the interior of the plywood through the coating, thereby improving the antibacterial properties. Deionized water and hydrochloric acid solution are added to calcium nitrate and triethyl phosphate ethanol, stirred to form a gel, and subsequently calcined to obtain a nano-calcium-phosphate bioceramic. The high specific surface area of ​​the quaternary ammonium salt provides a large number of attachment sites for the quaternary ammonium salt. After subsequent slow release, the positive charge of the quaternary ammonium salt adsorbs the negatively charged cell wall of E. coli, destroying the membrane structure and causing leakage of cell contents. Furthermore, the nanosilver slowly releases silver ions, destroying the cell membrane and DNA, inhibiting the growth of E. coli, achieving antibacterial persistence.

[0051] In Comparative Example 6, the quaternary ammonium salt-loaded nanoceramics are not added twice, but are directly added in the end-capping and cross-linking reaction process. The initial antibacterial activity is comparable to that of Example 3, but the organic residues of the ceramic defects reduce the fixation of didodecyldimethylammonium chloride and KH-550, and the antibacterial rate decreases after cleaning; Comparative Example 7 has no nanoceramics, and the antibacterial activity depends on nanosilver. After cleaning, the silver ions are lost and the durability is poor; the didodecyldimethylammonium chloride in Comparative Example 8 is directly added without ceramic carrier loading. The physical adsorption of didodecyldimethylammonium chloride is unstable, the initial antibacterial rate is low, the loss is serious after cleaning, and the antibacterial persistence decreases; Comparative Example 8 In Example 9, the initial antibacterial property was maintained by nanosilver and didodecyldimethylammonium chloride, but there was no hydrophobic protection of hydrolyzed perfluorooctyltriethoxysilane, and the antibacterial persistence also decreased after multiple water washings; in Comparative Example 10, the initial antibacterial property was supported by nanosilver and didodecyldimethylammonium chloride, but there was no KH-550 cross-linking, the fixation of the antibacterial agent was poor, and the antibacterial persistence deteriorated; in Comparative Example 11, the temperature increased during the capping and cross-linking reaction was too high, which slightly reduced the fixation effect of the antibacterial agent and the antibacterial persistence was reduced; in Comparative Example 12, there was no nanosilver and nanoceramics, only a polyurethane matrix without an antibacterial agent, and the antibacterial property and persistence were significantly reduced.

[0052] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention 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 the polyurethane liquid A is cooled, perfluorooctyltriethoxysilane liquid B is added dropwise to the polyurethane liquid A to react to form a fluorosilicone-terminated polyurethane; modified quaternary ammonium salt-loaded nanoceramics are added to the fluorosilicone-terminated polyurethane, stirred for reaction, and finally a coupling agent and a catalyst are added, the temperature is raised, the reaction is carried out, and the pressure is reduced to obtain a blocked polyurethane; Adding nanosilver, the modified quaternary ammonium salt-loaded nanoceramics, polyvinyl pyrrolidone and a defoaming agent to the blocked polyurethane, stirring and adjusting the viscosity to obtain the antibacterial coating for plywood; The polyurethane A liquid is obtained through prepolymerization reaction and chain extension reaction; The modified quaternary ammonium salt loaded nano ceramic is prepared by a sol-gel method to obtain nano calcium phosphate ceramics and then loaded with quaternary ammonium salt.

2. The method for preparing an antibacterial coating for plywood according to claim 1, characterized in that: The prepolymerization process is as follows: under nitrogen protection, 1,4-butanediol and 4,4'-methylenebis(phenyl isocyanate) are added, and the temperature is raised and stirred for reaction.

3. The method for preparing an antibacterial coating for plywood according to claim 1, characterized in that: The chain extension reaction process is as follows: cooling the prepolymer obtained by the prepolymerization reaction, adding a sodium 2,4-diaminobenzenesulfonate solution to stir the reaction, adding N,N-dimethylformamide to dilute the viscosity, adding isophorone diisocyanate, and heating the reaction.

4. The method for preparing an antibacterial coating for plywood according to claim 1, characterized in that: The preparation method of the perfluorooctyltriethoxysilane liquid B is as follows: perfluorooctyltriethoxysilane is added to ethanol and deionized water, and hydrochloric acid is added to carry out a hydrolysis reaction. After the reaction is completed, the perfluorooctyltriethoxysilane liquid B is obtained by filtering, drying, and redissolving.

5. The method for preparing an antibacterial coating for plywood according to claim 1, characterized in that: The sol-gel method comprises the following steps: adding calcium nitrate and triethyl phosphate into ethanol to form a uniform solution; adding hydrochloric acid into the uniform solution for hydrolysis and polycondensation to obtain a gel, and drying to obtain a dry gel; and subjecting the dry gel to programmed temperature and then calcining to obtain the nano calcium phosphate ceramic.

6. The method for preparing an antibacterial coating for plywood according to claim 5, characterized in that: The programmed temperature rising conditions are as follows: starting from 80° C., rising to 150-220° C. at a heating rate of 5° C. / min, maintaining for 15-40 minutes, and then rising to 450-600° C. and sintering for 1 hour.

7. The method for preparing an antibacterial coating for plywood according to claim 1, characterized in that: The process of loading the quaternary ammonium salt is as follows: the nano calcium phosphate ceramic is dispersed in ethanol, didodecyldimethylammonium chloride and gamma-aminopropyltriethoxysilane are added, stirred at room temperature, centrifuged, washed, and dried.

8. An antibacterial coating for plywood, characterized by: The antibacterial coating is prepared by the preparation method according to any one of claims 1 to 7; the raw materials for preparing the antibacterial coating include polyurethane liquid A, perfluorooctyltriethoxysilane liquid B, and quaternary ammonium salt-loaded nanoceramics; the viscosity of the antibacterial coating is 100-150 mPa·s; the antibacterial coating is used on the plywood as follows: pretreating the surface of the plywood, polishing with sandpaper to remove surface wax and impurities, and wiping with ethanol to clean it; using a spraying process to evenly spray the antibacterial coating on the surface of the plywood, with the coating thickness controlled to be 30-50 μm; finally, curing in a 60°C oven for 30 minutes, and naturally curing at room temperature to obtain a dry antibacterial coating.

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