Decorative paper with antibacterial function and preparation process thereof

Abstract

The present application belongs to the technical field of papermaking and functional material composite, and in particular relates to a decorative paper with antibacterial function and a preparation process thereof. The present application discloses a scheme named "a decorative paper with antibacterial function and a preparation process thereof", aiming to solve the problems of uneven dispersion, uncontrollable release and poor antibacterial durability of existing antibacterial agents in decorative paper. The decorative paper comprises a decorative base paper layer, an embedded antibacterial functional layer and a surface cross-linked protective layer; wherein the embedded layer is composed of amino-modified mesoporous silica microspheres loaded with nano-zinc oxide / quaternary ammonium salt chitosan composite antibacterial agent and modified melamine formaldehyde resin, and presents a spatial gradient distribution; the surface layer is cross-linked and solidified by a silane coupling agent to form a dense protective film. The structure realizes the dual mechanism of humidity-responsive controlled release and contact sterilization, while ensuring the physical properties and appearance of the decorative paper, providing broad-spectrum and long-lasting antibacterial effect, with an antibacterial rate of ≥99.5% in 24 hours, and the antibacterial rate still >95% after 50 times of wiping or 12 months of aging.

Description

Technical Field

[0001] This invention belongs to the field of papermaking and functional material composite technology, specifically, it relates to a decorative paper with antibacterial function and its preparation process. Background Technology

[0002] Decorative paper, a functional material widely used in furniture finishing, interior decoration, and building panel surfaces, not only serves a decorative purpose to enhance appearance but also possesses multiple functional attributes such as wear resistance, light resistance, flame retardancy, and even hygiene protection in specific usage environments. In recent years, with the significant increase in public health awareness and increasingly stringent requirements for the microbial safety of living environments, endowing decorative paper with durable, efficient, and environmentally friendly antibacterial properties has become an important direction for technological evolution in this field. Against this backdrop, developing new decorative paper products that combine excellent decorative effects with reliable antibacterial functions not only aligns with the development trend of green building materials but also has practical significance for preventing cross-infection and improving the hygiene of public and private spaces.

[0003] Currently, the main technical approaches to achieving antibacterial function in decorative paper focus on introducing inorganic or organic antibacterial agents into the paper base or impregnation resin system. Inorganic antibacterial agents, such as nano-silver, zinc oxide, and titanium dioxide, are widely used due to their broad-spectrum antibacterial properties and relatively stable chemical properties. Another type relies on organic compounds such as quaternary ammonium salts and triclosan, achieving antibacterial effects by disrupting microbial cell membranes or interfering with their metabolic processes. Specifically, existing processes typically pre-disperse these antibacterial components in impregnation melamine-formaldehyde resin or urea-formaldehyde resin, and then fix them onto the surface or internal structure of the decorative base paper through impregnation, drying, and hot pressing. This method, to a certain extent, integrates antibacterial functions and effectively alleviated the problem of microbial growth on the surface of decorative materials in early applications, meeting the initial market demand for basic hygiene performance at that time.

[0004] However, with the continuous development of related technologies and the increasingly stringent requirements for performance indicators in application scenarios, some inherent characteristics of the above-mentioned technical solutions at the principle level have gradually revealed their deep-seated limitations in addressing new challenges. Fundamentally, this stems from an inherent contradiction between the method of introducing antibacterial agents and their stability, release behavior, and compatibility with the matrix material in the composite system. On the one hand, to ensure the immediacy and broad-spectrum antibacterial effect, it is often necessary to increase the loading of antibacterial agents. However, this can easily lead to abnormally high viscosity of the resin system, decreased storage stability, and even discoloration, precipitation, or migration due to excessively high local concentrations during hot pressing, severely affecting the uniformity of the decorative paper's appearance and its physical and mechanical properties. On the other hand, if microencapsulation or surface modification is used to improve dispersion stability, it may hinder the effective release of antibacterial active ingredients, making it difficult for them to continuously contact and kill attached microorganisms in the actual use environment, resulting in a waste of resources and functional failure due to "high addition, low efficiency." Furthermore, some organic antibacterial agents are prone to degradation under prolonged light or high-temperature environments, resulting in a rapid decline in their antibacterial efficacy and the potential release of harmful byproducts, posing potential environmental and health risks. Correspondingly, while inorganic antibacterial agents offer better stability, their mechanisms of action largely rely on the slow dissolution of metal ions. Their antibacterial efficiency significantly decreases in low-humidity or non-aqueous environments, making them unsuitable for diverse indoor climate conditions. In addition, existing processes generally lack the ability to precisely control the spatial distribution of antibacterial agents within the paper-based three-dimensional network, leading to their enrichment on the surface and depletion in the interior. Once the surface is damaged due to wear or cleaning, the antibacterial function is rapidly lost, failing to achieve a long-lasting and balanced protective effect.

[0005] Therefore, how to construct a composite structure that can achieve efficient loading, stable anchoring and controlled release of antibacterial components without sacrificing the basic physical properties and aesthetic characteristics of decorative paper, and ensure its long-lasting, broad-spectrum and safe antibacterial ability in complex use environments, has become a key challenge and a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] This invention provides a decorative paper with antibacterial function and its preparation process, aiming to solve the technical problems in the prior art, such as uneven dispersion, poor stability, uncontrollable release, rapid decay of antibacterial efficacy, and negative impact on the physical properties and appearance of decorative paper. To achieve the above-mentioned objective, this invention constructs a multi-level composite structure system, forming an antibacterial functional phase with spatial gradient distribution characteristics within and on the surface of the decorative paper's fiber network. Combined with a specific chemical anchoring mechanism and a microenvironment-responsive release control strategy, this achieves broad-spectrum, long-lasting, and safe antibacterial performance while ensuring the mechanical strength, thermoforming properties, and color fidelity of the decorative paper.

[0007] The decorative paper with antibacterial function includes a decorative base paper, an embedded antibacterial functional layer, and a surface cross-linking protective layer. The decorative base paper is made from wood pulp fiber, cotton pulp fiber, or a mixture thereof using a wet papermaking process, with a basis weight of 60–120 g / m² and a thickness of 0.15–0.30 mm. Its internal pore structure is pretreated to form a three-dimensional network with a gradient pore size distribution, a pore size range of 5–50 μm, and a porosity of not less than 45%. The embedded antibacterial functional layer is composed of mesoporous silica microspheres loaded with a composite antibacterial agent and modified melamine-formaldehyde resin, uniformly distributed in the fiber gaps and pores of the decorative base paper, accounting for 3.5%–8.0% of the total mass of the decorative paper. The surface cross-linking protective layer is formed by thermosetting melamine-formaldehyde resin containing a silane coupling agent, with a thickness of 8–15 μm and a surface roughness Ra value controlled within the range of 0.2–0.6 μm.

[0008] The composite antibacterial agent is composed of nano-zinc oxide and quaternary ammonium salt functionalized chitosan in a mass ratio of (2.5:1) to (4.0:1). The nano-zinc oxide has a particle size of 20–40 nm, a specific surface area of ​​45–65 m² / g, and a hexagonal wurtzite crystal structure. The quaternary ammonium salt functionalized chitosan is prepared by dissolving chitosan in an aqueous acetic acid solution and reacting it with 3-chloro-2-hydroxypropyltrimethylammonium chloride at 60°C for 4 hours. Its degree of substitution is 0.85–1.15, and its molecular weight is 150,000–250,000 Da. The composite process employs an in-situ deposition method, where an aqueous solution of quaternary ammonium salt functionalized chitosan is dropwise added to a nano-zinc oxide dispersion. The mixture is stirred and reacted for 2 hours at a pH of 5.5–6.5 and a temperature of 45°C, allowing chitosan molecules to coat the surface of the nano-zinc oxide through electrostatic adsorption and coordination, forming core-shell structured composite particles.

[0009] The mesoporous silica microspheres have an average particle size of 300–500 nm, a pore size of 6–10 nm, a specific surface area of ​​800–1000 m² / g, and a pore volume of 0.9–1.2 cm³ / g; their surface is modified with 3-aminopropyltriethoxysilane, with a grafting density of 2.0–3.5. The composite antibacterial agent is loaded into the pores of mesoporous silica microspheres at a loading rate of 18%–25%, and is initially fixed through hydrogen bonds and weak covalent interactions between amino groups and the surface functional groups of the composite antibacterial agent. Subsequently, the mesoporous silica microspheres loaded with the composite antibacterial agent are mixed with modified melamine-formaldehyde resin at a mass ratio of 1:3 to 1:5 to form an antibacterial resin dispersion. The modified melamine-formaldehyde resin is obtained by introducing 5%–8% molar ratio of γ-glycidyl etheroxypropyltrimethoxysilane during the conventional synthesis of melamine-formaldehyde prepolymer. Its solid content is 55%–65%, its viscosity is 120–180 mPa·s (25℃), and its free formaldehyde content is less than 0.1%.

[0010] The formation process of the embedded antibacterial functional layer is as follows: The antibacterial resin dispersion is applied to the pre-wetted decorative base paper substrate by impregnation for 30-60 seconds, with a liquid retention rate of 80%-120%; subsequently, it is pre-dried at 80-100℃ for 3-5 minutes to allow the resin to initially penetrate and anchor within the fiber network; during this process, the mesoporous silica microspheres are trapped in pores at different depths due to the size effect, forming a spatial gradient distribution with decreasing concentration from the surface to the interior, and the microsphere density in the surface region (depth 0-30 μm) is 1.8 × 10⁻⁶. 6 ~2.5×10 6 The number of cells / mm³ is 1.0 × 10⁻⁶ in the middle layer (depth 30–80 μm). 6 ~1.7×10 6 The number of particles per mm³ is 0.3 × 10⁻⁶ for deeper regions (depth > 80 μm). 6 ~0.8×10 6 pcs / mm³.

[0011] The formation of the surface cross-linked protective layer adopts a two-stage impregnation process: after the construction of the embedded antibacterial functional layer is completed, the decorative paper is immersed again in a melamine-formaldehyde resin solution containing 0.8% to 1.5% by mass of N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, with the liquid content controlled at 40% to 60%, and then subjected to thermosetting treatment at 110 to 130°C for 90 to 150 seconds; during this process, the silane coupling agent hydrolyzes and condenses to form a three-dimensional silicon-oxygen network, and undergoes cross-linking reaction with the epoxy and amino groups in the underlying resin to generate a dense and chemically stable surface structure; this surface layer not only effectively inhibits the uncontrolled migration of internal antibacterial components, but also endows the material with immediate contact bactericidal ability due to the quaternary ammonium groups rich in its surface.

[0012] The preparation process specifically includes the following steps: Step 1: Preparation of quaternary ammonium salt functionalized chitosan; Chitosan with a degree of deacetylation ≥90% was dissolved in a 1% aqueous acetic acid solution to prepare a 2% (w / w) solution; Under nitrogen protection, 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, with a molar amount 1.2 times that of the chitosan glucose unit; The temperature was raised to 60℃, the pH was adjusted to 8.0, and the reaction was carried out for 4 hours; After the reaction was completed, the mixture was precipitated with anhydrous ethanol, filtered, washed until neutral, and vacuum dried to obtain quaternary ammonium salt functionalized chitosan; Step 2: Preparation of core-shell structured composite antibacterial agent; Disperse nano-zinc oxide in deionized water and sonicate for 30 minutes to form a stable suspension; Adjust the pH to 6.0, and slowly add the quaternary ammonium salt functionalized chitosan aqueous solution obtained in Step 1, the mass of which is 40% to 60% of the nano-zinc oxide; Stir the reaction at 45°C for 2 hours; Centrifuge, wash three times with water, and vacuum dry at 60°C to obtain the composite antibacterial agent; Step 3: Preparation of amino-modified mesoporous silica microspheres; Tetraethyl orthosilicate, hexadecyltrimethylammonium bromide, ammonia and ethanol were mixed in proportion and mesoporous silica microspheres were synthesized by sol-gel method; after calcination to remove the template agent, the microspheres were dispersed in toluene, 3-aminopropyltriethoxysilane was added, and the mixture was refluxed for 12 hours; the mixture was filtered, washed with toluene, and dried at 80℃ to obtain amino-modified mesoporous silica microspheres; Step 4: Loading the composite antibacterial agent; Dissolve the composite antibacterial agent obtained in Step 2 in an ethanol-water mixed solvent (volume ratio 3:1), add the mesoporous silica microspheres obtained in Step 3, ultrasonically disperse for 30 minutes, stir and adsorb at 40℃ for 6 hours; centrifuge, wash with ethanol, and dry at 60℃ to obtain the loaded antibacterial microspheres; Step 5: Synthesize modified melamine-formaldehyde resin; add formaldehyde aqueous solution (37%) and melamine in a reaction vessel at a molar ratio of 2.8:1, adjust the pH to 8.5 with sodium hydroxide, and heat to 85℃ to react until the cloud point; then cool to 60℃, add γ-glycidoxypropyltrimethoxysilane, which accounts for 6% of the melamine molar amount, and continue the reaction for 1 hour; adjust the pH to 7.5 with formic acid, cool to room temperature, and obtain the modified resin; Step 6: Prepare antibacterial resin dispersion; Mix the supported antibacterial microspheres obtained in Step 4 with the modified resin obtained in Step 5 at a mass ratio of 1:4, add 0.3% defoamer and 0.5% wetting agent, and disperse at high speed for 30 minutes to obtain a uniform dispersion; Step 7: First impregnation and pre-drying; After pre-wetting the decorative base paper with a basis weight of 80 g / m² and a thickness of 0.22 mm with deionized water, it is impregnated in the dispersion obtained in Step 6, with the liquid carry-over rate controlled at 100% and the impregnation time at 45 seconds; then it is placed in an 85℃ hot air drying oven and dried for 4 minutes to obtain a semi-finished product; Step 8: Secondary impregnation and heat curing; The semi-finished product is immersed in a melamine-formaldehyde resin solution containing 1.2% N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, with a liquid content of 50% and an impregnation time of 20 seconds; then it is placed in a 120℃ hot press, with a pressure of 0.3 MPa and a curing time of 120 seconds to obtain the finished decorative paper.

[0013] The finished decorative paper, tested according to GB / T 21510-2008 standard, showed an antibacterial rate of no less than 99.5% against Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 8739) within 24 hours. After 50 simulated cleaning wiping cycles (using an aqueous solution containing 0.5% sodium dodecylbenzenesulfonate, applying a pressure of 2 kPa, and a reciprocating frequency of 60 times / minute), the antibacterial rate remained above 95%. After being stored for 12 months in an environment with a relative humidity of 30%–80% and a temperature of 10℃–40℃, the antibacterial performance decreased by no more than 5%. Its surface abrasion resistance (CS-10 wheel, 1 kg load) was no less than 400 revolutions, and its gloss (60°) was 15–35 GU, meeting the requirements of GB / T 15102-2017 impregnated film paper-faced artificial board standard.

[0014] Furthermore, 0.5% to 1.2% cationic starch is added to the decorative base paper during the papermaking process to enhance the positive charge density on the fiber surface and promote the electrostatic adsorption and positioning distribution of subsequent mesoporous silica microspheres; the degree of substitution of the cationic starch is 0.03 to 0.06, and the gelatinization temperature is 62 to 68°C.

[0015] In a preferred embodiment of the present invention, the nano zinc oxide is modified with sodium citrate before composite formation, so that its zeta potential is adjusted from +18 mV to -22 mV, thereby enhancing the electrostatic attraction between it and the positively charged quaternary ammonium salt functionalized chitosan, and improving the coating efficiency and structural stability.

[0016] During the thermosetting process, the silane coupling agent in the surface cross-linking protective layer not only cross-links with the underlying resin, but also partially hydrolyzes with moisture in the air to form a surface silanol-rich layer. This layer can adsorb trace amounts of moisture in the usage environment, maintain local microenvironment humidity, thereby activating the photocatalytic activity of nano zinc oxide. Even under weak indoor light conditions, it can continuously generate active oxygen species, working synergistically with quaternary ammonium salts to achieve a dual sterilization mechanism.

[0017] During the service life of the decorative paper, the mesoporous silica microspheres in the embedded antibacterial functional layer release the composite antibacterial agent within their pores in a controlled manner through a humidity-responsive mechanism: when the relative humidity of the environment is higher than 60%, the chitosan molecular chains absorb water and swell, the pores expand, and the diffusion of antibacterial components is accelerated; when the humidity is lower than 40%, the chitosan shrinks, the pores close, and the release rate is inhibited. This mechanism ensures that the release is enhanced in high-humidity environments where microorganisms are prone to grow, and the release is slowed down in dry environments, thereby extending the overall antibacterial lifespan.

[0018] During the hot-pressing process, the surface cross-linked protective layer of the decorative paper undergoes a dehydration condensation reaction with the hydroxyl groups on the surface of the artificial board substrate, forming a strong chemical bond interface. This prevents the antibacterial functional layer from being exposed or failing due to interlayer peeling. At the same time, the bonding force of this interface is tested by ASTM D903, and the peel strength is not less than 4.5 N / mm.

[0019] In summary, this invention fundamentally solves the technical contradictions of uneven dispersion, uncontrollable release, poor durability, and impact on substrate performance of traditional decorative paper antibacterial agents by constructing a four-in-one antibacterial functional system of "gradient distribution - chemical anchoring - microenvironment response release - surface contact sterilization", thus achieving a high degree of unity between decoration, functionality, and durability. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the decorative paper with antibacterial function according to the present invention.

[0021] Figure 2 This is a schematic diagram of the spatial gradient distribution of the embedded antibacterial functional layer in the decorative paper base layer of the present invention.

[0022] Figure 3 This is a schematic diagram of the core-shell structure of the composite antibacterial agent of the present invention.

[0023] Figure 4 This is a schematic diagram of the structure of the mesoporous silica microspheres loaded with composite antibacterial agents according to the present invention.

[0024] Figure 5 This is a partially enlarged schematic diagram of the interface bonding between the surface cross-linked protective layer and the underlying resin and substrate of the present invention.

[0025] Figure 6 This is a schematic diagram of the preparation process of the present invention.

[0026] Figure 7 This is a schematic diagram illustrating the antibacterial agent release mechanism of the decorative paper of the present invention under different humidity conditions. Detailed Implementation

[0027] This invention provides a decorative paper with antibacterial function and its preparation process. The technical solution involves constructing a multi-level composite structure system to form an antibacterial functional phase with spatial gradient distribution characteristics within and on the surface of the decorative paper's fiber network. Combined with a specific chemical anchoring mechanism and a microenvironment-responsive release control strategy, this achieves broad-spectrum, long-lasting, and safe antibacterial properties while ensuring the decorative paper's mechanical strength, thermoforming properties, and color fidelity. The technical solution of this invention will be described in detail below with reference to specific embodiments.

[0028] The decorative paper with antibacterial function includes a decorative base paper layer, an embedded antibacterial functional layer, and a surface cross-linked protective layer. The decorative base paper layer is made from wood pulp fiber, cotton pulp fiber, or a mixture thereof using a wet-process papermaking method, with a basis weight of 60–120 g / m² and a thickness of 0.15–0.30 mm. In one specific embodiment, softwood pulp and hardwood pulp are mixed at a mass ratio of 7:3, and after beating to a Canadian standard free fraction (CSF) of 420 mL, 0.8% cationic starch is added as a retention aid. The degree of substitution of this cationic starch is 0.045, and the gelatinization temperature is 65°C. The basis weight of the decorative base paper obtained by papermaking is 80 g / m², and the thickness is 0.22 mm. Its internal pore structure is pretreated to form a three-dimensional network with a gradient pore size distribution. The pore size ranges from 5 to 50 μm, and the porosity is measured to be 48.3%. The pore size distribution measured by mercury intrusion porosimetry shows a bimodal characteristic, with the main peaks located at 12 μm and 35 μm, corresponding to the interfiber bundle gaps and micropores between individual fibers, respectively.

[0029] The embedded antibacterial functional layer is composed of mesoporous silica microspheres loaded with a composite antibacterial agent and modified melamine-formaldehyde resin, uniformly distributed in the fiber gaps and pores of the decorative base paper substrate, accounting for 3.5% to 8.0% of the total mass of the decorative paper. In this embodiment, the functional layer accounts for 5.7% of the total mass. The composite antibacterial agent is composed of nano-zinc oxide and quaternary ammonium salt functionalized chitosan in a mass ratio of 3.2:1. The nano-zinc oxide has a particle size of 32 nm (statistical average value of transmission electron microscopy), a specific surface area of ​​58 m² / g, and X-ray diffraction pattern shows that its crystal structure is hexagonal wurtzite type with no impurity phase peaks. Quaternary ammonium salt functionalized chitosan was prepared by dissolving chitosan with a degree of deacetylation of 92% in a 1% aqueous acetic acid solution to a 2% (w / w) concentration. Under nitrogen protection, 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, with a molar amount 1.2 times that of the chitosan glucose units. The mixture was heated to 60°C, and the pH was adjusted to 8.0 with sodium hydroxide solution. The reaction was allowed to proceed for 4 hours. After the reaction, the product was precipitated with anhydrous ethanol, filtered, washed with deionized water until neutral (pH=7.0), and vacuum dried at 60°C for 12 hours to obtain a white flocculent product. Elemental analysis and ¹H-NMR determination showed a degree of substitution of 1.02 and a molecular weight of 198,000 Da (GPC determination, using dextran as a standard).

[0030] The composite antibacterial agent was prepared using an in-situ deposition method: 30 g of nano-zinc oxide was dispersed in 500 mL of deionized water and sonicated for 30 minutes (300 W, 40 kHz) to form a stable suspension; the pH was adjusted to 6.0 with dilute hydrochloric acid; a solution of 12 g of the above-mentioned quaternary ammonium salt functionalized chitosan dissolved in 100 mL of deionized water was slowly added dropwise, and the mixture was stirred at 300 rpm for 2 hours at 45 °C; the mixture was then centrifuged (8000 rpm, 15 minutes), washed three times with water, and vacuum dried at 60 °C to obtain a grayish-white powdery composite antibacterial agent. Scanning electron microscopy showed that chitosan uniformly coated the surface of the nano-zinc oxide, forming a core-shell structure with a shell thickness of approximately 8–12 nm. Zeta potential testing showed that the surface potential of the composite particles changed from +18 mV to -15 mV, confirming the successful coating of chitosan.

[0031] Mesoporous silica microspheres were prepared using the sol-gel method: 10 mL of tetraethyl orthosilicate (TEOS), 2.5 g of hexadecyltrimethylammonium bromide (CTAB), 4 mL of ammonia (25%), and 100 mL of anhydrous ethanol were mixed and stirred at room temperature for 24 hours. The resulting precipitate was centrifuged, washed with ethanol, and calcined in a muffle furnace at 550 °C for 6 hours to remove the template agent, yielding white mesoporous silica microspheres. The average particle size was 420 nm (measured by dynamic light scattering), the pore size was 8.3 nm (BET method), the specific surface area was 920 m² / g, and the pore volume was 1.05 cm³ / g. Subsequently, amino modification was performed: 5 g of the above microspheres were dispersed in 100 mL of toluene, and 1.2 mL of 3-aminopropyltriethoxysilane (APTES) was added. The mixture was refluxed under nitrogen protection for 12 hours. After filtration, the microspheres were washed three times with toluene and dried at 80 °C to obtain amino-modified mesoporous silica microspheres. The surface amino grafting density was determined to be 2.8 mmol / g by acid-base titration.

[0032] The loading process of the composite antibacterial agent was as follows: 8 g of the composite antibacterial agent was dissolved in 80 mL of ethanol-water mixed solvent (volume ratio 3:1), and 40 g of amino-modified mesoporous silica microspheres were added. After ultrasonic dispersion for 30 minutes, the mixture was stirred at 200 rpm at 40℃ for 6 hours for adsorption. After centrifugation, the microspheres were washed three times with ethanol and dried at 60℃ to obtain the loaded antibacterial microspheres. Thermogravimetric analysis (TGA) showed that the loading rate was 21.3%, i.e., 0.213 g of composite antibacterial agent was loaded per gram of microspheres. The infrared spectrum showed an amide I band at 1650 cm⁻¹ and an N–H bending vibration peak at 1560 cm⁻¹, confirming that the composite antibacterial agent successfully entered the pores. At the same time, hydrogen bonds were formed between the amino groups on the surface of the microspheres and the hydroxyl / carboxyl groups of chitosan, achieving preliminary fixation.

[0033] The synthesis steps of modified melamine-formaldehyde resin are as follows: In a 5 L reactor equipped with a condenser, thermometer, and stirrer, 1800 g (22.2 mol) of 37% formaldehyde aqueous solution and 1260 g (10 mol) of melamine were added. The pH was adjusted to 8.5 with 30% sodium hydroxide solution, and the temperature was raised to 85℃ to react to the cloud point (about 90 minutes). Then, the temperature was lowered to 60℃, and 19.2 g (0.06 mol, accounting for 6% of the molar amount of melamine) of γ-glycidoxypropyltrimethoxysilane (KH-560) was added, and the reaction was continued for 1 hour. The pH was adjusted to 7.5 with 10% formic acid solution, and the mixture was cooled to room temperature to obtain a pale yellow transparent liquid. The resin had a solid content of 60.2% (measured after drying at 105℃ for 2 hours), a viscosity of 152 mPa·s (at 25℃, using a rotational viscometer), and a free formaldehyde content of 0.07% (determined by the acetylacetone method).

[0034] Preparation of antibacterial resin dispersion: 10 kg of supported antibacterial microspheres were mixed with 40 kg of the above-mentioned modified melamine-formaldehyde resin, and 30 g of silicone defoamer (BYK-024) and 50 g of fluorocarbon wetting agent (Capstone FS-30) were added. The mixture was sheared at 2500 rpm for 30 minutes in a high-speed disperser to obtain a uniform, sediment-free milky white dispersion. Laser particle size analysis showed that the D50 of the microspheres in the resin was 435 nm, and the distribution width (Span) was 0.82, indicating good dispersion stability.

[0035] The first impregnation and pre-drying process involved pre-wetting decorative base paper (80 g / m² basis weight, 0.22 mm thickness) with deionized water spray (moisture content controlled at 15% ± 1%), followed by continuous immersion in the antibacterial resin dispersion at a linear velocity of 1.2 m / min for 45 seconds. The liquid carry-over rate was precisely controlled to 100% (i.e., 100% paper weight gain) using roller pressure. The paper was then dried in an 85℃ hot air drying oven for 4 minutes, allowing the resin to initially penetrate and anchor within the fiber network. During this process, because the mesoporous silica microspheres (420 nm) have a much larger particle size than the smallest micropores (5 μm) in the decorative base paper's base layer, the microspheres could not penetrate the dense surface layer and were trapped in pores at different depths, forming a spatial gradient distribution with decreasing concentration from the surface inwards. The cross-section was analyzed using focused ion beam scanning electron microscopy (FIB-SEM) three-dimensional reconstruction technology, and the microsphere density in the surface region (depth 0–30 μm) was measured to be 2.1 × 10⁻⁶. 6 The number of cells / mm³ is 1.4 × 10⁻⁶ in the middle layer (depth 30–80 μm). 6 The number of particles per mm³ is 0.5 × 10⁻⁶ for deeper regions (depth > 80 μm). 6 The number of pieces per mm³ meets the design gradient requirements.

[0036] Secondary impregnation and thermosetting process: The above semi-finished product was immersed at a linear velocity of 1.0 m / min into a melamine-formaldehyde resin solution (solid content 58%) containing 1.2% N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane (KH-602) for 20 seconds, with the liquid content controlled at 50%. It was then placed in a 120℃ flatbed hot press under a pressure of 0.3 MPa for 120 seconds. During this process, KH-602 first hydrolyzes to generate silanol, which then undergoes a ring-opening reaction with the epoxy groups in the underlying modified resin, and simultaneously condenses with amino groups to form –Si–O–C– and –Si–N– bonds; in addition, self-condensation also occurs between silanols, forming a three-dimensional silicon-oxygen network. The resulting surface cross-linked protective layer thickness was 11.3 μm (measured by a profilometer), and the surface roughness Ra value was 0.42 μm (measured by a stylus profilometer, measuring length 4 mm), which meets the design range of 0.2–0.6 μm.

[0037] The final decorative paper product was tested according to GB / T 21510-2008 "Test Method for Antibacterial Properties of Nano-Inorganic Materials". The 24-hour inhibition rates against Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 8739) were 99.7% and 99.6%, respectively. Durability testing employed a simulated cleaning and wiping experiment: the non-woven fabric was impregnated with an aqueous solution containing 0.5% sodium dodecylbenzenesulfonate, and a pressure of 2 kPa was applied. The surface was wiped 50 times at a frequency of 60 times / minute, and the inhibition rate was tested again, yielding results of 95.8% (Staphylococcus aureus) and 96.1% (Escherichia coli). Long-term stability testing involved storing the sample in a climate chamber with a relative humidity of 30%–80% and a temperature of 10℃–40℃ for 12 months. Monthly sampling was conducted to test the inhibition rate. After 12 months, the inhibition rate decreased to 4.2%, still remaining above 95.4%. In terms of physical properties, the surface abrasion resistance (CS-10 wheel, 1 kg load) is 432 revolutions, and the gloss (60°) is 24 GU, both of which meet the requirements of GB / T 15102-2017 "Impregnated Paper Faced Wood-based Panels" standard.

[0038] Furthermore, during the thermosetting process of the surface cross-linked protective layer, some unreacted silane coupling agent hydrolyzes with moisture in the air, forming a surface silanol-rich layer. X-ray photoelectron spectroscopy (XPS) analysis shows that in the Si 2p peak of the surface layer, the Si–OH component accounts for 38%, while Si–O–Si accounts for only 62%. This hydroxyl-rich layer can adsorb trace amounts of moisture (equilibrium moisture content of approximately 1.8%) in the usage environment, maintaining local microenvironment humidity, thereby activating the photocatalytic activity of nano-zinc oxide. Even under low-light conditions indoors (illuminance ≤300 lux, main wavelength 400–700 nm), electron paramagnetic resonance (EPR) detection can still capture ·OH and ·O2⁻ signals, confirming the continuous generation of reactive oxygen species and the synergistic effect with the contact bactericidal effect of quaternary ammonium salts.

[0039] Mesoporous silica microspheres embedded in the antibacterial functional layer exhibited humidity-responsive release behavior during service. The release of quaternary ammonium salts from chitosan was monitored by high-performance liquid chromatography (HPLC) after placing the supported antibacterial microspheres in different humidity environments. The results showed that the cumulative release over 24 hours was 2.1% at 30% relative humidity; increased to 5.8% at 60% humidity; and reached 9.3% at 80% humidity. This phenomenon is attributed to the hydrophilicity of the chitosan molecular chains—high humidity causes water absorption and swelling, leading to expansion of mesoporous channels and accelerated diffusion of antibacterial components; low humidity causes chain segment contraction and pore closure, inhibiting release. This mechanism ensures enhanced release in high-humidity environments conducive to microbial growth and slowed release in dry environments, thereby extending the overall antibacterial lifespan.

[0040] In hot-press lamination applications, the decorative paper of this invention is hot-pressed with a particleboard substrate at 120°C and 0.8 MPa for 30 seconds. Residual amino and silanol groups in the surface cross-linked protective layer undergo dehydration condensation with the cellulose hydroxyl groups on the substrate surface, forming chemical bonds such as –Si–O–Cellulose– and –NH–CO–Cellulose–. Peel strength testing according to ASTM D903 standard shows an interfacial bonding strength of 4.8 N / mm, far exceeding the industry standard requirement of 3.0 N / mm, effectively preventing interlayer peeling that could expose or cause failure of the antibacterial functional layer.

[0041] In a preferred embodiment of the present invention, the nano-zinc oxide is surface-modified with sodium citrate before composite processing: 30 g of nano-zinc oxide is dispersed in 500 mL of deionized water, 1.5 g of sodium citrate is added, and the mixture is sonicated for 30 minutes and stirred at 60°C for 2 hours; after centrifugation, washing with water, and drying, the zeta potential is adjusted from +18 mV to -22 mV. This negatively charged surface significantly enhances the electrostatic attraction between the nano-zinc oxide and the positively charged quaternary ammonium salt functionalized chitosan (zeta potential +28 mV), increasing the coating efficiency from 82% to 95% and reducing the core-shell structure detachment rate by 60% in subsequent processing.

[0042] To verify the superiority of the technical solution of the present invention, the following comparative examples are provided: Comparative Example 1: Antibacterial decorative paper was prepared using a conventional physical blending method. Unloaded nano-zinc oxide (30 nm) and quaternary ammonium salt functionalized chitosan were directly added to melamine-formaldehyde resin at a mass ratio of 3.2:1, with the remaining processes the same as in the Example. The resulting product initially exhibited an antibacterial rate of 98.2%, but this decreased to 82.5% after 20 wipes and further declined to 76.3% after 12 months; noticeable white spots appeared on the surface, the gloss level was only 8 GU, and the abrasion resistance was 280 revolutions.

[0043] Comparative Example 2: The gradient distribution design was omitted, and the loaded antibacterial microspheres were only coated on the paper surface. The remaining components and processes were the same as in the Example. The initial antibacterial rate was 99.5%, but there was no antibacterial ability in the deeper layers; the surface layer was easy to peel off after hot pressing, and the peel strength was only 2.1 N / mm; the initial release was too fast under high humidity conditions, and the antibacterial rate decreased by 12% within 3 months.

[0044] Comparative Example 3: Unmodified melamine-formaldehyde resin was used, without silane coupling agent. The rest was the same as in the examples. The surface crosslinking density was low, with an Ra value of 1.2 μm and a wear resistance of only 210 revolutions; the antibacterial agent migrated severely, and the antibacterial rate dropped to 89.7% after 10 wipes.

[0045] Comparing the key performance data of the embodiments with those of the comparative examples, the data show that the present invention significantly improves the antibacterial durability, physical and mechanical properties and interfacial bonding strength of decorative paper through the synergistic effect of multi-level structural design, chemical anchoring, gradient distribution and microenvironment response release, overcoming the defects of traditional methods such as uneven dispersion, uncontrollable release, poor durability and impact on appearance.

[0046] In summary, the decorative paper with antibacterial function and its preparation process provided by this invention achieve a high degree of unity between decoration, functionality, and durability by precisely controlling the chemical structure, spatial distribution, and interaction mechanism of each component. Those skilled in the art can make adaptive adjustments to the raw material ratios, process parameters, and equipment selection based on the above embodiments without departing from the core idea of ​​this invention; all such adjustments should be considered within the protection scope of this invention.

Claims

1. A decorative paper with antibacterial function, characterized in that, The material comprises a decorative base paper, an embedded antibacterial functional layer, and a surface cross-linking protective layer. The decorative base paper is made from wood pulp fiber, cotton pulp fiber, or a mixture thereof using a wet-process papermaking method, with a basis weight of 60–120 g / m² and a thickness of 0.15–0.30 mm. Its internal pore structure has a three-dimensional network with a gradient pore size distribution, a pore size range of 5–50 μm, and a porosity of not less than 45%. The embedded antibacterial functional layer is composed of mesoporous silica microspheres loaded with a composite antibacterial agent and modified melamine-formaldehyde resin, uniformly distributed in the fiber gaps and pores of the decorative base paper, accounting for 3.5%–8.0% of the total weight of the decorative paper. The surface cross-linking protective layer is formed by thermosetting melamine-formaldehyde resin containing a silane coupling agent, with a thickness of 8–15 μm and a surface roughness Ra value of 0.2–0.

6. μm; wherein, the composite antibacterial agent is composed of nano-zinc oxide and quaternary ammonium salt functionalized chitosan in a mass ratio of (2.5:1) to (4.0:1), the nano-zinc oxide has a particle size of 20–40 nm, a specific surface area of ​​45–65 m² / g, and a hexagonal wurtzite crystal structure; the quaternary ammonium salt functionalized chitosan has a degree of substitution of 0.85–1.15 and a molecular weight of 150,000–250,000 Da; the mesoporous silica microspheres have an average particle size of 300–500 nm, a pore size of 6–10 nm, a specific surface area of ​​800–1000 m² / g, a pore volume of 0.9–1.2 cm³ / g, and their surface is modified with 3-aminopropyltriethoxysilane with a grafting density of 2.0–3.

5. The composite antibacterial agent is loaded into the pores of mesoporous silica microspheres at a loading rate of 18%–25%. The modified melamine-formaldehyde resin is obtained by introducing 5%–8% molar ratio of γ-glycidyl etheroxypropyltrimethoxysilane during the synthesis of melamine-formaldehyde prepolymer, with a solid content of 55%–65%, a viscosity of 120–180 mPa·s (25℃), and a free formaldehyde content of less than 0.1%.

2. The decorative paper with antibacterial function according to claim 1, characterized in that, The mesoporous silica microspheres in the embedded antibacterial functional layer are spatially gradient distributed in the decorative base paper substrate, with a microsphere density of 1.8 × 10⁻⁶ within a depth range of 0–30 μm in the surface region. 6 ~2.5×10 6 The density of microspheres in the middle layer region (depth range of 30–80 μm) is 1.0 × 10⁻⁶ / mm³. 6 ~1.7×10 6 The density of microspheres in the deep region (depth greater than 80 μm) is 0.3 × 10⁻⁶ / mm³. 6 ~0.8×10 6 pcs / mm³.

3. The decorative paper with antibacterial function according to claim 1, characterized in that, The quaternary ammonium salt functionalized chitosan was prepared by dissolving chitosan in an aqueous acetic acid solution and reacting it with 3-chloro-2-hydroxypropyltrimethylammonium chloride at 60°C for 4 hours. The composite antibacterial agent was prepared by in-situ deposition, in which an aqueous solution of quaternary ammonium salt functionalized chitosan was added dropwise to a nano zinc oxide dispersion and stirred for 2 hours at a pH of 5.5-6.5 and a temperature of 45°C, so that chitosan molecules were coated on the surface of the nano zinc oxide to form core-shell structured composite particles.

4. The decorative paper with antibacterial function according to claim 1, characterized in that, The surface cross-linked protective layer is formed by two impregnations and thermal curing of a melamine-formaldehyde resin solution containing 0.8% to 1.5% by mass of N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane; the thermal curing conditions are 110 to 130°C and 90 to 150 seconds; the surface cross-linked protective layer is formed by a three-dimensional silicon-oxygen network through hydrolysis and condensation of a silane coupling agent, which cross-links with the epoxy and amino groups in the underlying resin and forms a silicon-rich hydroxyl layer on the surface.

5. The decorative paper with antibacterial function according to claim 1, characterized in that, The decorative base paper substrate has 0.5% to 1.2% cationic starch added during the papermaking process, the degree of substitution of the cationic starch is 0.03 to 0.06, and the gelatinization temperature is 62 to 68°C.

6. The decorative paper with antibacterial function according to claim 3, characterized in that, The nano zinc oxide was modified with sodium citrate before composite formation, which adjusted its zeta potential from +18 mV to -22 mV to enhance its electrostatic adsorption with quaternary ammonium salt functionalized chitosan.

7. The decorative paper with antibacterial function according to claim 1, characterized in that, The mesoporous silica microspheres in the embedded antibacterial functional layer achieve controlled release of antibacterial agents during service through a humidity response mechanism: when the relative humidity of the environment is higher than 60%, the chitosan molecular chains absorb water and swell, causing the pores to expand and accelerating the diffusion of antibacterial components; when the relative humidity of the environment is lower than 40%, the chitosan molecular chains contract, causing the pores to close and inhibiting the release of antibacterial components.

8. The decorative paper with antibacterial function according to claim 1, characterized in that, During the hot-pressing process, the surface cross-linked protective layer undergoes a dehydration condensation reaction with the hydroxyl groups on the surface of the engineered wood substrate to form –Si–O–Cellulose– and –NH–CO–Cellulose– chemical bonds, with an interfacial peel strength of not less than 4.5 N / mm.

9. The decorative paper with antibacterial function according to claim 1, characterized in that, The finished decorative paper exhibits a 24-hour antibacterial rate of no less than 99.5% against Staphylococcus aureus ATCC 6538 and Escherichia coli ATCC 8739; after 50 simulated cleaning and wiping cycles, the antibacterial rate remains above 95%; after being stored for 12 months in an environment with a relative humidity of 30%–80% and a temperature of 10℃–40℃, the antibacterial performance decreases by no more than 5%; the surface abrasion resistance is no less than 400 revolutions, and the gloss is 15–35 GU.

Images