Water-based coating with sound insulation and antibacterial functions and preparation method thereof

Abstract

The present application relates to the functional coating technical field, disclose a kind of water-based paint with sound insulation and antibacterial function and its preparation method, by comprising the following weight parts of raw materials are made: anionic water-based polyurethane emulsion 60 to 90 parts;Multi-functional group modified lignin 10 to 40 parts;Volatility charge shielding agent 0.5 to 3.0 parts;Water-based auxiliary 0.1 to 5.0 parts;Deionized water balance;The multi-functional group modified lignin is the lignin derivative grafted with long-chain alkyl, hydrophilic polyether segment and cationic guanidino group;The volatility charge shielding agent is shielded by ion competition adsorption under liquid state Cationic charge of the multi-functional group modified lignin, and volatilize to remove shielding in the process of drying into film, cause multi-functional group modified lignin and anionic water-based polyurethane emulsion occur ion lock, solve the colloidal stability problem when cationic modified lignin and anionic water-based polyurethane emulsion are blended.

Description

Technical Field

[0001] This invention relates to the field of functional coatings technology, specifically to a water-based coating with both sound insulation and antibacterial functions, and its preparation method. Background Technology

[0002] With increasingly stringent environmental regulations and rising living standards, waterborne coatings, due to their low volatile organic compound emissions, have gradually replaced solvent-based coatings as the mainstream material in building decoration and transportation. Among them, anionic waterborne polyurethane is widely used as a film-forming base material for waterborne coatings due to its excellent film-forming properties, flexibility, and adhesion. To meet the demands of modern applications for environmental comfort and hygiene, introducing components with acoustic damping and antibacterial functions into waterborne polyurethane systems has become a research hotspot.

[0003] Industrial lignin, an abundant natural aromatic polymer, possesses excellent mechanical damping properties due to its rigid benzene ring skeleton and complex network structure, making it an ideal filler for preparing sound-insulating and noise-reducing coatings. To further impart antibacterial activity to the coatings, lignin typically requires chemical modification by introducing cationic groups such as quaternary ammonium salts or guanidine groups. However, this modification strategy faces serious challenges in practical applications regarding colloidal chemical stability. Since most commercially available waterborne polyurethane emulsions are carboxylic acid or sulfonic acid anionic emulsions, the direct addition of cationically modified lignin with a high density of positive charges can cause the strong electrostatic attraction between opposite charges to instantly disrupt the electric double layer on the surface of the latex particles. This leads to irreversible charge neutralization, resulting in rapid flocculation, demulsification, and even precipitation of the emulsion, failing to meet the storage stability requirements of the coating products.

[0004] To address the compatibility issues of blends of anionic and cationic polymers, existing technologies typically employ the addition of large amounts of nonionic surfactants or polymeric dispersants to maintain the metastable state of the system. However, this method of adding small-molecule additives has significant drawbacks: on the one hand, residual hydrophilic surfactants significantly increase the water absorption rate of the final coating, leading to decreased water resistance, easy whitening, and weakening of the interaction forces between polymer molecular chains, thus reducing the physical and mechanical strength of the coating; on the other hand, due to the lack of effective chemical bonding or strong interaction anchoring, antibacterial components easily migrate to the surface with moisture and are lost after the coating dries, making it difficult to achieve long-lasting antibacterial effects. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a water-based coating with both sound insulation and antibacterial functions, as well as its preparation method, solving the problems of low strength and easy loss of the antibacterial layer in existing coatings.

[0006] In a first aspect, the present invention provides a water-based coating that combines sound insulation and antibacterial functions, employing the following technical solution:

[0007] A water-based coating with both sound insulation and antibacterial functions is made from the following raw materials in parts by weight: 60 to 90 parts of anionic waterborne polyurethane emulsion; 10 to 40 parts of multifunctional modified lignin; 0.5 to 3.0 parts of volatile charge shielding agent; 0.1 to 5.0 parts of waterborne additives; and the balance being deionized water. The multifunctional modified lignin is a lignin derivative grafted with long-chain alkyl groups, hydrophilic polyether segments, and cationic guanidine groups. The volatile charge shielding agent shields the cationic charge of the multifunctional modified lignin in the liquid state through ion competitive adsorption, and releases the shielding by volatilization during the drying and film-forming process, thereby promoting ion locking between the multifunctional modified lignin and the anionic waterborne polyurethane emulsion.

[0008] By adopting the above technical solution, this invention solves the compatibility problem of anionic and cationic polymer blends by utilizing the phase change characteristics of volatile salts and polymer structure design, and constructs an interpenetrating network structure. The specific mechanism is as follows:

[0009] First, regarding the colloidal stability mechanism of the system: During the liquid storage stage, the anions dissociated from the volatile charge-shielding agent preferentially adsorb around the cationic guanidine groups of the modified lignin, compressing the electric double layer and shielding its positive potential. Simultaneously, the hydrophilic polyether segments on the surface of the modified lignin extend in the aqueous phase, providing steric hindrance. This synergistic effect of electrostatic shielding and steric hindrance prevents direct contact between the modified lignin cations and the aqueous polyurethane anionic particles, thus preventing flocculation of the emulsion during mixing and storage.

[0010] Secondly, regarding the mechanical reinforcement and long-lasting antibacterial mechanism: During the coating drying and film-forming stage, as moisture evaporates, the volatile charge-shielding agent decomposes and escapes, the shielding layer disappears, and the cationic guanidine groups on the modified lignin are exposed. These groups then undergo Coulombic interactions with the carboxylate anions on the waterborne polyurethane molecular chains, forming ionic cross-linking points. This in-situ ion-locking effect anchors the modified lignin in the polyurethane matrix, improving the tensile strength and water resistance of the coating, and restricting the migration of antibacterial groups, thus achieving long-lasting antibacterial effects.

[0011] Finally, regarding the damping mechanism: the rigid benzene ring framework of the multifunctional modified lignin serves as the hard core of the dispersed phase, while the grafted long-chain alkyl groups act as flexible side chains. Under acoustic or mechanical vibration, the internal friction between the flexible chain segments and the matrix converts mechanical energy into heat energy. This microstructure, with its rigid framework support and flexible side chains dissipating energy, endows the coating with acoustic damping properties.

[0012] Preferably, the volatile charge shielding agent is selected from at least one of ammonium carbonate, ammonium bicarbonate, or ammonium acetate.

[0013] By adopting the above technical solution, such weak acid and weak base salts have specific decomposition temperatures and volatility characteristics. They provide ionic strength to maintain dispersion stability in a liquid state at room temperature. During the drying and film formation process, they decompose without leaving small molecule salts in the coating, thereby avoiding negative impacts on the coating's water resistance and gloss.

[0014] Preferably, the long-chain alkyl group in the multifunctional modified lignin is derived from C12 to C16 alkyl glycidyl ether, and the hydrophilic polyether segment is derived from epoxy polyethylene glycol with a number average molecular weight Mn of 600 to 2000.

[0015] By adopting the above technical solution, the alkyl chain lengths from C12 to C16 are suitable, which can both improve the damping factor through the energy dissipation of chain segment friction and provide hydrophobicity to balance the coating's resistance to water whitening. The polyether segments with a number average molecular weight (Mn) of 600 to 2000 can provide appropriate steric hindrance to maintain emulsion stability, while avoiding an increase in coating water absorption due to excessively long hydrophilic segments.

[0016] Preferably, the aqueous additives include film-forming aids, wetting and leveling agents, and defoamers, wherein the film-forming aids are selected from dipropylene glycol butyl ether, dipropylene glycol methyl ether, or dodecyl alcohol ester.

[0017] By adopting the above technical solution, the selected film-forming aid can reduce the minimum film-forming temperature of polyurethane latex particles, promote particle deformation and fusion, and form a dense coating film.

[0018] Preferably, the solid content of the anionic aqueous polyurethane emulsion is 35% to 50%, and the pH value of the finished coating is 7.5 to 9.0.

[0019] By adopting the above technical solution, the pH value can be controlled within the weakly alkaline range, which can maintain the chemical stability of the volatile charge shielding agent, prevent it from decomposing prematurely during the storage period, and ensure the storage life of the coating.

[0020] Secondly, the present invention provides a method for preparing a water-based coating that combines sound insulation and antibacterial functions, using the following technical solution:

[0021] A method for preparing a water-based coating with both sound insulation and antibacterial functions includes the following steps:

[0022] S1. Disperse the multifunctional modified lignin in deionized water, add a volatile charge shielding agent, and stir until ionic equilibrium is established to obtain a modified lignin premix solution with cation shielding.

[0023] S2. Under shearing and stirring conditions, the modified lignin premix obtained in step S1 is added dropwise to the anionic aqueous polyurethane emulsion to obtain a stable intermediate emulsion.

[0024] S3. Add water-based additives to the intermediate emulsion obtained in step S2, adjust the viscosity, and filter to obtain the finished water-based coating.

[0025] By employing the above technical solution, this method achieves dispersion through stepwise control of the ionic environment. In step S1, ionic equilibrium is pre-established to suppress the cation potential of the modified lignin. In step S2, the local ion concentration is controlled by dropwise addition to avoid the impact caused by instantaneous contact between high charge density components. This process reduces the interfacial tension during mixing of opposite charges, achieving uniform dispersion of modified lignin in the waterborne polyurethane system.

[0026] Preferably, in step S1, the specific control conditions for establishing ion balance are: controlling the stirring speed to 300 rpm to 600 rpm, the stirring time to 30 minutes to 60 minutes, and adjusting the pH value of the premixed solution to 7.8 to 8.5.

[0027] By adopting the above technical solution, the control of stirring parameters ensures that the shielding agent is fully dissolved and diffused; the control of pH value inhibits the hydrolysis of the shielding agent and maintains the stability of the shielding environment.

[0028] Preferably, in step S1, when the multifunctional modified lignin contains C16 or higher long-chain alkyl groups, the dissolution process is carried out under warm conditions of 40°C to 50°C, and after complete dissolution, the temperature is lowered to room temperature before adding the volatile charge shielding agent.

[0029] By adopting the above technical solution, the warm conditions promote the stretching of the molecular chains of long-chain alkyl-modified lignin and improve the dispersion efficiency; after cooling, the addition of a shielding agent prevents the decomposition of heat-sensitive salts.

[0030] Preferably, step S2 is implemented as follows: the anionic aqueous polyurethane emulsion is placed in a dispersion vessel, the rotation speed is set to 800 rpm to 1200 rpm, and the modified lignin premix is ​​added dropwise at a rate of 5 parts / minute to 10 parts / minute, while maintaining the system in an emulsion state with a bluish tint during the dropwise addition.

[0031] By adopting the above technical solution, high shear speed combined with low-speed droplet addition enables the droplets entering the system to disperse rapidly and prevent local agglomeration; the bluish emulsion state indicates that the micro-particles are uniform in size, which is used as a process control indicator to ensure the fineness of the coating.

[0032] Preferably, the multifunctional modified lignin is pre-prepared by the following method: after dissolving alkali lignin, it is grafted with long-chain alkyl epoxy ether, epoxy polyethylene glycol and polyhexamethylene guanidine hydrochloride in sequence at 70°C to 90°C in the presence of a phase transfer catalyst. After the reaction is completed, it is purified by dialysis and dried to obtain the lignin.

[0033] By employing the above technical solution, phase transfer catalysis is used to reduce the reaction interface energy, enabling the grafting of multiple functional groups. The long-chain alkyl groups introduced in the reaction impart damping properties to the product, epoxy-based polyethylene glycol provides steric hindrance, and polyhexamethylene guanidine hydrochloride imparts antibacterial properties and ion-locking ability to the product. This stepwise grafting strategy regulates the hydrophilicity-hydrophobicity balance and charge density of lignin, providing a material basis for the stability and performance improvement of the coating system.

[0034] This invention provides a water-based coating with both sound insulation and antibacterial functions, and its preparation method. It has the following beneficial effects:

[0035] 1. This invention solves the problem of colloidal stability when blending cationic modified lignin with anionic waterborne polyurethane emulsions by introducing a volatile charge-shielding agent. During liquid storage, the volatile charge-shielding agent utilizes an ion competition mechanism to suppress electrostatic attraction between opposite charges, preventing emulsion flocculation. During the drying and film-forming period, the agent decomposes and volatilizes, inducing in-situ ionic crosslinking between the cationic guanidine groups on the modified lignin and the anionic groups on the polyurethane segments. This transition from liquid-state shielding to solid-state crosslinking significantly improves the coating's water resistance and physical and mechanical strength while ensuring storage stability.

[0036] 2. The multifunctional modified lignin of this invention, through specific molecular structure design, endows the coating with excellent damping noise reduction and long-lasting antibacterial properties. The rigid phenylpropane skeleton of lignin and the grafted long-chain alkyl flexible side chains form a microstructure, which utilizes the internal friction between chain segments to convert acoustic mechanical energy into heat energy dissipation, thereby improving the damping factor. At the same time, the grafted polyhexamethylene guanidine groups serve as highly active antibacterial sites, which are anchored in the resin matrix network through ionic bonds, restricting the migration and precipitation of antibacterial agents, thus achieving long-lasting antibacterial properties throughout the entire life cycle of the coating.

[0037] 3. This invention employs a pre-established ion equilibrium combined with controlled shear dropwise addition preparation process, achieving uniform dispersion of high-filler-content modified lignin in an aqueous system. This process effectively controls the particle size distribution of latex particles, avoiding the problem of rough coating surface caused by local agglomeration, resulting in a coating with both good leveling properties and storage stability, overcoming the defects of traditional biomass modified coatings such as easy sedimentation and low gloss. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the preparation process of the present invention. Detailed Implementation

[0039] The technical solution of the present invention will now be clearly and completely described 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.

[0040] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products:

[0041] Anionic aqueous polyurethane emulsion: It is an aliphatic polyester or polyether polyurethane aqueous dispersion modified by hydrophilic chain extension of carboxylate or sulfonate. It is a semi-transparent to milky white liquid with a bluish tint, a solid content of 40%±2%, a pH value of 7.5-9.0, a viscosity of 50-300 mPa·s (25℃), a minimum film-forming temperature of less than 0℃, an elongation at break of ≥500%, and a tensile strength of ≥20MPa. In this embodiment, it serves as a film-forming matrix to provide anionic sites.

[0042] Alkali lignin: CAS No. 8068-05-1, derived from black liquor extraction in sulfate pulping, with a weight-average molecular weight (Mw) of 3000-8000 Da, a polydispersity index of 1.5-2.5, and a total hydroxyl content of 9.0-11.0 mmol / g, of which the phenolic hydroxyl content is 3.0-4.5 mmol / g, serving as a damping core for a rigid framework.

[0043] Polyhexamethylene guanidine hydrochloride: CAS No. 57028-96-3, number average molecular weight (Mn) is 800-1500 Da, active guanidine content is ≥95%, easily soluble in water, used as a cationic antibacterial agent and reaction precursor.

[0044] C12-C14 alkyl glycidyl ether: CAS No. 68609-97-2, epoxy equivalent is 275-300g / eq, the main component is a mixture of dodecyl glycidyl ether and tetradecyl glycidyl ether, used to introduce flexible hydrophobic side chains.

[0045] Methoxy polyethylene glycol glycidyl ether: CAS number is single fixed (polymer), number average molecular weight (Mn) is about 1000 Da, epoxy value ≥0.90 mmol / g, structure is a polyethylene glycol derivative with one end capped by methyl and the other end by glycidyl ether group, used to provide steric stabilization.

[0046] Other common reagents include: epichlorohydrin (CAS No. 106-89-8, purity ≥99.5%), tetrabutylammonium bromide (CAS No. 1643-19-2, analytical grade), ammonium carbonate (CAS No. 506-87-6, ammonia content ≥30.0%), dipropylene glycol butyl ether (CAS No. 29911-28-2, industrial grade), dimethyl sulfoxide (CAS No. 67-68-5, analytical grade), as well as commercially available industrial-grade polyether-modified polydimethylsiloxane defoamers and polyether-modified silicone leveling agents.

[0047] Preparation Example 1: This preparation example provides a method for preparing modified multifunctional lignin G-PEG-AL-1, including the following steps:

[0048] 100g of dried alkali lignin with a total hydroxyl content of approximately 1000mmol was dissolved in 300g of dimethyl sulfoxide (DMSO). The solution was heated to 60℃ and stirred until completely dissolved. 0.8g of tetrabutylammonium bromide was added as a phase transfer catalyst. 20g of C12-C14 alkyl glycidyl ether and 10g of methoxy polyethylene glycol glycidyl ether were added dropwise to the solution. The solution was heated to 90℃ and reacted at a constant temperature for 5 hours to graft the flexible alkyl chain and hydrophilic PEG segment onto the lignin backbone.

[0049] (2) End epoxidation: Cool the reaction solution to 60°C, add 50g epichlorohydrin (about 540mmol), and add 20% sodium hydroxide aqueous solution dropwise to maintain the pH of the system at 10-11. React for 4 hours. After the reaction is completed, distill under reduced pressure at 60°C and -0.09MPa for 30 minutes to remove unreacted epichlorohydrin and obtain an intermediate solution containing active epoxy groups. The main solvent is still DMSO.

[0050] (3) Antibacterial functionalization: 300g of deionized water was added to the above intermediate solution for dilution and dispersion, followed by the addition of 75g of an aqueous solution of polyhexamethylene guanidine hydrochloride with a solid content of 40%, i.e., 30g of pure PHMG, about 170mmol repeating unit. The pH of the system was adjusted to 9.0-9.5, and the temperature was raised to 80℃ for 6 hours to allow the amino groups on PHMG to undergo a ring-opening addition reaction with the epoxy groups on lignin.

[0051] (4) Purification: After the reaction is completed, the product solution is put into a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed in flowing deionized water for 48 hours to remove the solvent DMSO, small molecule salts and unreacted free PHMG. The dialyzed solution is freeze-dried to obtain a reddish-brown solid product, which is denoted as G-PEG-AL-1.

[0052] Preparation Example 2: This preparation example provides a method for preparing modified multifunctional lignin G-PEG-AL-2, mainly used to verify the effect of a high proportion of flexible hydrophobic side chains on damping performance, including the following steps:

[0053] The operating procedure was basically the same as in Preparation Example 1, except that the raw material feeding ratio was different in step (1): the amount of C12-C14 alkyl glycidyl ether was adjusted to 35g (about 122mmol), while the amount of methoxy polyethylene glycol glycidyl ether remained unchanged at 10g. The amounts of epichlorohydrin and polyhexamethylene guanidine hydrochloride and all reaction conditions in the subsequent steps were the same as in Preparation Example 1, and a solid product was finally obtained, denoted as G-PEG-AL-2.

[0054] Preparation Example 3: This preparation example provides a method for preparing modified multifunctional lignin G-PEG-AL-3, mainly used to verify the effect of a high proportion of hydrophilic steric hindrance chains on the stability of the system, including the following steps:

[0055] The operation steps were basically the same as those in Preparation Example 1, except that the raw material feeding ratio in step (1) was different: the amount of methoxy polyethylene glycol glycidyl ether was adjusted to 25g, while the amount of C12-C14 alkyl glycidyl ether remained unchanged at 20g. The subsequent steps and reaction conditions were the same as in Preparation Example 1, and a solid product was finally obtained, denoted as G-PEG-AL-3.

[0056] Preparation Example 4: This preparation example provides a method for preparing modified multifunctional lignin G-PEG-AL-4, mainly used to verify the effect of high-density cationic grafting rate on antibacterial properties, including the following steps:

[0057] The operation steps were basically the same as those in Preparation Example 1, except that the raw material feeding ratio in step (3) was different: the amount of aqueous solution of polyhexamethylene guanidine hydrochloride was adjusted to 125g, with a solid content of 40%, i.e., 50g of pure PHMG, approximately 280mmol of repeating unit. The raw material amounts in the remaining steps, including the amount of epichlorohydrin and the reaction conditions, remained unchanged. The final product was a solid product, denoted as G-PEG-AL-4.

[0058] Preparation Example 5: This preparation example provides a method for preparing modified multifunctional lignin G-PEG-AL-5 to verify the universality of alkyl side chains with different chain lengths, including the following steps:

[0059] The procedure was basically the same as in Preparation Example 1, except that in step (1), 20 g of cetyl glycidyl ether (C16-GE, Mw~340, about 59 mmol) was used instead of C12-C14 alkyl glycidyl ether, while the amounts of other raw materials and reaction conditions remained unchanged. The final product was a solid product, denoted as G-PEG-AL-5.

[0060] Comparative Preparation Example 1: This comparative preparation example provides a modified lignin D-AL-1 lacking flexible damping side chains, comprising the following steps:

[0061] The operation steps are basically the same as those in Preparation Example 1, except that in step (1), C12-C14 alkyl glycidyl ether is not added, but only 10g of methoxy polyethylene glycol glycidyl ether is added for grafting; subsequent steps (2), (3), and (4) are exactly the same. The final product is a solid product, denoted as D-AL-1.

[0062] Comparative Preparation Example 2: This comparative preparation example provides a modified lignin D-AL-2 lacking a hydrophilic steric hindrance chain, comprising the following steps:

[0063] The operation steps were basically the same as those in Preparation Example 1, except that in step (1), methoxy polyethylene glycol glycidyl ether was not added, and only 20g of C12-C14 alkyl glycidyl ether was added for grafting; subsequent steps (2), (3), and (4) were exactly the same. The final product was a solid product, denoted as D-AL-2.

[0064] Example 1: This example provides a water-based coating with both sound insulation and antibacterial functions, and its preparation method. The modified lignin G-PEG-AL-1 obtained in Example 1 is used as the key component. (Refer to Appendix) Figure 1 This includes the following steps:

[0065] (1) Preparation and charge shielding of modified lignin solution: Take 20 parts (by weight, the same below) of the dried solid modified lignin G-PEG-AL-1 obtained in Preparation Example 1, add it to 80 parts of deionized water, and stir at room temperature until completely dissolved to obtain a modified lignin aqueous solution with a solid content of 20%. Add 1.5 parts of ammonium carbonate solid to the solution, stir at 500 rpm for 45 minutes to completely dissolve the ammonium carbonate and establish ionic equilibrium, and adjust the pH of the solution to 8.0 to obtain a cationic lignin premixed solution treated with charge shielding.

[0066] (2) Emulsion compounding: 70 parts of anionic aqueous polyurethane emulsion were placed in a dispersion vessel, and the dispersion disc speed was set to 1000 rpm. All the cationic lignin premixed solution obtained in step (1) above was slowly added dropwise to the aqueous polyurethane emulsion at a rate of 5 parts / minute. During the dropwise addition, it was observed that the system always maintained a bluish emulsion state, and no obvious flocculation or precipitation was produced.

[0067] (3) Additive dispersion and finished product: After the addition is complete, reduce the rotation speed to 500 rpm, and add 2.0 parts of dipropylene glycol butyl ether, 0.3 parts of polyether-modified polydimethylsiloxane defoamer, and 0.3 parts of polyether-modified silicone leveling agent to the system in sequence. Continue stirring for 30 minutes, let it stand to defoam, and then filter it through a 200-mesh nylon filter to obtain the finished water-based coating.

[0068] Example 2: This example provides a water-based coating with both sound insulation and antibacterial functions, aiming to verify the effect of high-filler-content modified lignin (G-PEG-AL-2) on the system's stability and damping performance, including the following steps:

[0069] (1) Preparation of modified lignin solution and charge shielding: Take 30 parts of the dried solid modified lignin G-PEG-AL-2 obtained in Preparation Example 2 and add it to 120 parts of deionized water to prepare an aqueous solution with a solid content of 20%. Considering the increase in the content of cationic components, add 2.5 parts of ammonium carbonate solid to the solution, stir for 60 minutes, and adjust the pH value to 8.2 to obtain a premixed solution treated with charge shielding.

[0070] (2) Emulsion compounding: Take 60 parts of anionic aqueous polyurethane emulsion (solid content 40%) and place it in a dispersion vessel. Set the rotation speed to 1200 rpm. Slowly add all the premixed liquid (152.5 parts in total, containing 30 parts of dry weight lignin) obtained in step (1) above to the polyurethane emulsion. Due to the high solid content and viscosity, extend the mixing time appropriately until the addition is complete, and continue high-speed dispersion for 20 minutes.

[0071] (3) Additive dispersion and finished product: Reduce the rotation speed, add 2.5 parts of dipropylene glycol butyl ether, 0.4 parts of defoamer and 0.4 parts of leveling agent, stir to disperse evenly and filter to obtain high damping waterborne coating.

[0072] Example 3: This example provides a water-based coating with both sound insulation and antibacterial functions, using modified lignin G-PEG-AL-4 with high antibacterial activity, and verifies its performance at low addition levels, including the following steps:

[0073] (1) Preparation of modified lignin solution and charge shielding: Take 10 parts of the dried solid modified lignin G-PEG-AL-4 obtained in Preparation Example 4 and add it to 40 parts of deionized water to prepare a 20% solution. Add 0.8 parts of ammonium carbonate solid, stir for 30 minutes, and adjust the pH value to 7.8 to obtain a premixed solution.

[0074] (2) Emulsion compounding: Take 85 parts of anionic aqueous polyurethane emulsion (solid content 40%) and place it in a dispersion vessel, rotating at 800 rpm. Add the above premixed solution (total 50.8 parts) dropwise.

[0075] (3) Additive dispersion and finished product: Add 1.5 parts of dipropylene glycol butyl ether, 0.2 parts of defoamer and 0.2 parts of leveling agent, mix evenly and filter to obtain a high-transparency water-based coating.

[0076] Example 4: This example provides a water-based coating with both sound insulation and antibacterial functions, verifying the feasibility of using different types of volatile weak acid and weak base salts as shielding agents, including the following steps:

[0077] (1) Preparation of modified lignin solution and charge shielding: Take 20 parts of the dried solid modified lignin G-PEG-AL-1 obtained in Preparation Example 1 and dissolve it in 80 parts of deionized water. Add 2.0 parts of ammonium bicarbonate to the solution instead of ammonium carbonate, stir in a sealed container at room temperature for 60 minutes, and adjust the pH value to 7.8.

[0078] (2) Emulsion compounding and finished product: Take 70 parts of anionic waterborne polyurethane emulsion, add the premixed liquid treated with ammonium bicarbonate dropwise according to the process steps and additive dosage described in Example 1, mix evenly and filter to obtain the finished waterborne coating.

[0079] Example 5: This example provides a water-based coating with both sound insulation and antibacterial functions, using long-chain alkyl-modified lignin G-PEG-AL-5, including the following steps:

[0080] (1) Preparation of modified lignin solution and charge shielding: Take 20 parts of the dry solid modified lignin G-PEG-AL-5 obtained in Preparation Example 5, which contains C16 alkyl side chains, add it to 80 parts of deionized water, and assist in dissolution under a warming condition of 40°C. After cooling to room temperature, add 1.6 parts of ammonium carbonate and stir for 45 minutes to perform charge shielding.

[0081] (2) Emulsion compounding and finished product: Take 70 parts of anionic waterborne polyurethane emulsion and compound it according to the process steps and additive dosage described in Example 1. During the additive addition stage, add an appropriate amount of deionized water to adjust the viscosity to be similar to that in Example 1, and filter to obtain the finished waterborne coating.

[0082] Comparative Example 1: This comparative example provides an aqueous coating lacking a temperature-sensitive charge shielding process. Compared with Example 1, the difference is that component C is not added in step (1), and the modified lignin G-PEG-AL-1 is dissolved and the pH is adjusted to 8.0 before being directly added in step (2). The other raw materials and dosages are the same.

[0083] Note: Due to the lack of a shielding agent, this comparative ratio experienced severe flocculation during the mixing process, making it impossible to prepare a uniform coating. Therefore, there is no subsequent performance test data, and only process phenomena are recorded.

[0084] Comparative Example 2: This comparative example provides an aqueous coating that uses physical blending instead of chemical grafting. The difference from Example 1 is that the product of Preparation Example 1 is not used in step (1). Instead, equal amounts of unmodified alkali lignin, hydrolyzed C12-C14 alkyl glycerol ether, methoxy polyethylene glycol and polyhexamethylene guanidine hydrochloride (PHMG) are directly physically mixed, and 1.0 part of emulsifier is added to assist dispersion. The remaining process steps and additives are the same.

[0085] Comparative Example 3: This comparative example provides an aqueous coating lacking a flexible damping side chain. The difference from Example 1 is that in step (1), D-AL-1 (ungrafted long-chain alkyl) obtained from Comparative Preparation Example 1 is used instead of G-PEG-AL-1, and all other steps are the same.

[0086] Comparative Example 4: This comparative example provides an aqueous coating lacking a hydrophilic steric hindrance chain. The difference from Example 1 is that in step (1), D-AL-2 (ungrafted PEG) obtained from Comparative Preparation Example 2 was used instead of G-PEG-AL-1, and all other steps were the same.

[0087] Comparative Example 5: This comparative example provides a commonly used physical filler functional coating. Compared with Example 1, the difference is that no lignin derivatives and temperature-sensitive shielding agents are used; in step (2), 15 parts of hollow glass microspheres and 5 parts of silver-loaded microcapsules are directly added to 70 parts of aqueous polyurethane emulsion and prepared by high-speed dispersion, with the amount of other additives being the same.

[0088] Test Example 1: Verification of the colloidal stability limit and film-forming crosslinking mechanism of the system

[0089] This test case mainly verifies the effectiveness of the temperature-sensitive charge shielding technology described in this invention in the liquid state, as well as the real existence of the in-situ ion locking mechanism after drying and film formation.

[0090] The finished coating emulsions prepared in Examples 1, 2, and 5, as well as the mixtures prepared in Comparative Example 2 (physical blending) and Comparative Example 4 (without PEG steric hindrance), were used as test samples. Comparative Example 1 was severely flocculated during preparation and could not be further tested; therefore, it was directly determined to have failed the stability test.

[0091] Each of the above samples was placed into a centrifuge tube and centrifuged at 4000 rpm for 30 minutes at an ambient temperature of 25°C using a high-speed refrigerated centrifuge. The upper emulsion was discarded, the mass of the bottom precipitate was weighed, and the centrifugal sedimentation rate (precipitate mass / total mass × 100%) was calculated to characterize the ultimate stability of the emulsion under a strong shear field.

[0092] Take 200g of each of the above groups of samples, place them in a sealed container, and put them in a 50℃ constant temperature forced air drying oven for accelerated thermal aging test. After storage for 168 hours (7 days), take them out, cool them to room temperature, and use a Stormer viscometer to test the viscosity values ​​before and after thermal storage, and calculate the viscosity change rate (|viscosity after aging - initial viscosity| / initial viscosity × 100%).

[0093] Each group of samples was coated onto a polytetrafluoroethylene mold and dried at room temperature for 7 days to constant weight, yielding a dry film with a thickness of approximately 0.5 mm. The mass W0 of the dry film was accurately weighed and placed in a Soxhlet extractor. Tetrahydrofuran was used as the solvent, and extraction was performed at 80 °C under reflux for 24 hours to remove soluble components that had not undergone chemical cross-linking or strong physical locking. After extraction, the remaining solid was removed and dried in a vacuum oven at 60 °C to constant weight. The mass W1 was weighed, and the gel fraction (GelFraction = W1 / W0 × 100%) was calculated to characterize the density of the cross-linked network after film formation.

[0094] Table 1. Statistical analysis of colloidal stability and gel fraction after film formation of the system.

[0095] Sample number Centrifugal sedimentation rate (%) Viscosity change rate of thermal storage at 50℃ (%) Gel fraction (%) Example 1 0.12 3.4 88.7 Example 2 0.19 4.8 91.2 Example 5 0.15 3.9 87.4 Comparative Example 2 0.86 6.2 34.5 Comparative Example 4 5.43 28.7 86.1

[0096] According to the data in Table 1, the example group and the comparative group showed significant differences in liquid stability and solid crosslinking, which directly confirms the dual-action mechanism proposed in this invention.

[0097] Regarding the temperature-sensitive shielding and steric stabilization mechanism in liquid, the centrifugal sedimentation rates of Examples 1, 2, and 5 were all below 0.2%, and the thermal storage viscosity change rate was controlled within 5%. This indicates that in the high ionic strength environment of ammonium carbonate, the metastable coexistence of high charge density cationic lignin and anionic polyurethane emulsion was successfully achieved through the steric hindrance provided by PEG segments and the competitive adsorption of NH4+ ions.

[0098] In contrast, although ammonium carbonate was added to Comparative Example 4 for charge shielding, the lack of hydrophilic PEG segments in the modified lignin molecular chain meant that the reduced electrostatic repulsion caused by the compression of the electric double layer under high-speed centrifugal fields or intensified thermal motion could not be compensated for by steric hindrance. This led to collisional aggregation of microparticles, resulting in a sedimentation rate as high as 5.43% and a dramatic increase in viscosity of 28.7%. Combined with the instantaneous flocculation phenomenon observed in Comparative Example 1 without the addition of a shielding agent, this confirms that ion shielding is fundamental, steric hindrance is a guarantee, and their synergistic effect is a necessary condition for achieving liquid stability in this system.

[0099] Regarding the in-situ ion-locking and interpenetrating polymer network mechanism in the solid state, gel fraction is a key indicator for measuring the crosslinking density of the polymer network. Comparative Example 2, using physical blending with no chemical bonds between components, had a gel fraction of only 34.5%, indicating that a large amount of ungrafted lignin, free PHMG, and small molecule additives failed to enter the polyurethane main network and were easily extracted and dissolved under the swelling effect of tetrahydrofuran solvent. In contrast, the gel fractions of the Example Groups all exceeded 87%, a high value confirming two levels of microstructural evolution: first, the epoxy groups on the modified lignin underwent partial covalent crosslinking with PHMG and potentially active groups in the matrix; second, and more importantly, during film formation, with the evaporation of moisture and the decomposition of the shielding agent (releasing NH3 and CO2), the shielded guanidino cations were re-exposed and interacted strongly with the carboxylate anions on the polyurethane chains through Coulombic forces. This in-situ ion-locking effect, combined with the physical entanglement of long-chain alkyl groups, constructs a high-density interpenetrating polymer network, firmly anchoring the modified components in the matrix and preventing extraction by good solvents. This structural difference is the material basis for the excellent washability, antibacterial properties, and high damping performance of the coating of this invention.

[0100] Test Example 2: Comprehensive Evaluation of Coating Mechanical, Acoustic Damping and Functional Durability

[0101] This test case aims to evaluate the overall application effect of the technical solution by comparing specific data on physical and mechanical properties, dynamic thermomechanical properties, and antibacterial long-term effects of embodiments with different modified structures and comparative examples lacking key features.

[0102] The coating samples prepared in Examples 1, 2, and 5, as well as Comparative Examples 2, 3, and 5, were cast into films in polytetrafluoroethylene molds. After drying at room temperature for 48 hours, they were placed in an oven at 60°C for 24 hours to obtain dry films with a thickness of approximately 1.0 mm, which were used for mechanical and damping tests. In addition, the above coatings were coated onto clean glass plates and fiber cement boards, with the dry film thickness controlled at 40 μm, for optical and antibacterial performance tests.

[0103] Using a universal testing machine, according to the GB / T17200 standard, the free membrane was cut into dumbbell-shaped strips and tested at a tensile speed of 50 mm / min. The tensile strength and elongation at break were recorded. Five parallel samples were tested for each group of samples and the average value was taken.

[0104] Damping performance was tested using a dynamic thermomechanical analyzer. The thin film stretching mode was used, with a frequency of 1 Hz, a heating rate of 3 ℃ / min, and a scanning temperature range of -50 ℃ to 100 ℃. The curve of loss factor (tanδ) changing with temperature was recorded, and the peak value of tanδ and the effective damping temperature range (the temperature range where tanδ>0.3) were extracted.

[0105] According to GB / T2410 standard, the transmittance of the coating on the glass plate was tested using a transmittance / haze meter; according to GB / T21866 standard, the antibacterial performance was tested. First, the initial antibacterial rate of each group of samples against Staphylococcus aureus and Escherichia coli was tested. Then, the sample surface was subjected to 500 wet scrubbing cycles using a scrubbing tester with a 0.5% sodium dodecylbenzene sulfonate solution as the medium. After rinsing and drying, the antibacterial rate after scrubbing was tested again.

[0106] Table 2. Test data on the comprehensive physical and mechanical properties and functional durability of the coating.

[0107] Sample number Tensile strength (MPa) Elongation at break (%) DMA loss factor peak value (tanδmax) Effective damping temperature range (°C) Light transmittance (%) Initial antibacterial rate (%) Antibacterial rate (%) after 500 washes Example 1 28.4 482 0.65 -12~63 91.2 >99.9 >99.9 Example 2 32.7 355 0.83 -8~76 86.5 >99.9 >99.9 Example 5 29.1 453 0.69 -16~68 90.8 >99.9 >99.9 Comparative Example 2 12.3 208 0.14 none 82.1 >99.9 18.4 Comparative Example 3 35.8 176 0.21 12~28 92.4 >99.9 >99.9 Comparative Example 5 15.2 115 0.17 none 12.6 >99.9 84.7

[0108] According to the data in Table 2, the example group, while maintaining a balance between high light transmittance and high strength, exhibited significantly better damping performance and antibacterial durability than the comparative example.

[0109] Regarding acoustic damping, the peak tanδ values ​​of Examples 1, 2, and 5 all exceeded 0.65, and their effective damping temperature range covered the normal operating range. In contrast, the peak tanδ value of Comparative Example 3 was only 0.21, and that of Comparative Example 5 was only 0.17. This confirms that the high damping characteristics of the present invention do not originate from the rigid structure of lignin itself, but rather from the flexible side-chain friction energy dissipation mechanism introduced by the grafted long-chain alkyl groups.

[0110] The data comparison between Example 1 and Comparative Example 3 directly shows that when acoustic energy is transmitted to the interior of the coating, the rigid lignin nucleus acts as a fixed point, and the grafted C12-C16 alkyl segments act as moving units. Under dynamic stress, strong internal molecular friction is generated, thereby converting mechanical energy into heat energy dissipation. However, Comparative Example 3 lacks this soft-hard coupling structure and exhibits rigid characteristics of high modulus but low loss.

[0111] Meanwhile, Example 2 further increased the density of friction units in the system by increasing the content of modified lignin, thereby raising the peak value of tanδ to 0.83, demonstrating the feasibility of achieving adjustable damping performance by adjusting grafting parameters.

[0112] In terms of mechanical properties and appearance, Example 1 exhibited an elongation at break of 482%, significantly higher than the 115% of Comparative Example 5. Comparative Example 5 used hollow glass microspheres as a physical sound-insulating filler. The interfacial bonding between the microspheres and the polymer matrix was weak, easily leading to stress concentration and premature matrix fracture under stress. Furthermore, the addition of the filler significantly reduced the light transmittance to 12.6%. In contrast, the embodiments of this invention formed a homogeneous interpenetrating polymer network through in-situ ion locking. Modified lignin was dispersed in the matrix at the molecular or nanoscale, without compromising the coating's transparency. The dynamic dissociation and recombination of ionic bonds effectively dissipated tensile energy, achieving a simultaneous improvement in strength and toughness. Comparative Example 2, due to the lack of chemical bonding between components and poor compatibility, suffered severe phase separation, resulting in low tensile strength and elongation.

[0113] Regarding functional durability, the antibacterial rate of Comparative Example 2 plummeted from >99.9% to 18.4% after 500 washes, indicating that the physically mixed PHMG is highly susceptible to migration and loss with water molecules. In contrast, the Example group maintained an antibacterial rate of >99.9% after washing with the same intensity. This result confirms the effectiveness of the chemical bonding mechanism constructed in this invention: PHMG is covalently grafted onto the lignin framework via an epoxy ring-opening reaction, and the lignin framework is locked within the cured polyurethane network through multi-point ionic bonds. This dual anchoring effect completely solves the problem of small-molecule antibacterial agent precipitation and failure, ensuring the functional stability of the coating under long-term use and frequent cleaning conditions.

[0114] Test Example 3: Coating Application Process and Environmental Aging Resistance Test

[0115] This test case aims to supplement and verify the sieving adaptability of the present invention in actual construction applications, as well as the stability of the film after formation under environmental erosion such as water and solvents, so as to comprehensively evaluate the robustness of the technical solution.

[0116] Filtration Residue Test: Take 500g of each of the coating samples prepared in Examples 1-5 and Comparative Examples 1-5, and filter them using a 200-mesh nylon filter of known mass. For samples that cannot pass through the filter, stop the test and record it as "filter blockage"; for samples that pass through smoothly, rinse the residue trapped on the filter with a small amount of deionized water, dry to constant weight, weigh, and calculate the residual fraction (ppm = residue mass mg / coating mass kg) to quantitatively evaluate the degree of emulsion demulsification and coarsening of the emulsion.

[0117] Water whitening resistance test: The filtered paint sample was coated onto a black glass plate and dried at room temperature for 7 days. Then, the sample was immersed in deionized water at 25°C for 96 hours. After removal, the surface moisture was dried, and the coating surface was observed for blistering or peeling. The color difference between the immersed and unimmersed areas was compared and recorded as "no change", "slight whitening" or "severe whitening".

[0118] Solvent resistance wiping test: According to GB / T23989 standard, use a cotton ball soaked in 75% ethanol solution to repeatedly wipe the cured coating surface with a load of 1 kgf, and record the number of wipings when the coating is exposed or damaged. If the coating is not damaged after 100 wipings, record it as ">100 times".

[0119] Table 3. Test data on coating application processability and environmental resistance of coating film

[0120] Sample number 200-mesh filter residue (ppm) Water whitening performance Ethanol wiping resistance (number of wipes) Remark Example 1 15 No change >100 Standard Formula Example 2 22 No change >100 High viscosity system is well dispersed Example 3 8 No change >100 Low addition amount, optimal dispersion Example 4 18 No change >100 Ammonium bicarbonate shielding is effective Example 5 25 No change >100 The C16 segment is highly hydrophobic. Comparative Example 1 (Traffic Jam Network) / / Severe flocculation, unable to be tested Comparative Example 2 35 Severe whitening 24 Physical blending, poor tolerance Comparative Example 3 12 Slightly white >100 It has no alkyl chain and is highly hydrophilic. Comparative Example 4 4500 / 85 Severe roughening, resulting in a rough coating. Comparative Example 5 45 Slightly white >100 There are micro-gaps in the interface

[0121] Based on the data in Table 3, a horizontal comparison of all embodiments and comparative examples further clarifies the contribution of the synergistic effect of each component of the present invention to process stability and finished product durability.

[0122] Regarding process adaptability, Comparative Example 1, lacking a charge-shielding agent, experienced instantaneous flocculation due to direct contact between anions and cations, preventing it from passing through the filter. This confirms that temperature-sensitive shielding is a prerequisite for the system's success. Comparative Example 4, although containing a shielding agent, lacked sufficient steric hindrance due to the absence of PEG segments grafted onto the modified lignin, resulting in micro-agglomeration during the dropwise addition process. The filtration residue reached a high of 4500 ppm, indicating a coarsening state that could not meet the fineness requirements of commercial coatings.

[0123] The residual amount of all examples (1-5) was controlled within 25 ppm. Among them, Example 3 had the lowest residual amount due to the low amount of modified component added (10 parts), which proves that the dual stabilization mechanism of charge shielding and steric hindrance adopted in this invention can ensure the high dispersion stability of the system under shear flow.

[0124] In terms of environmental resistance, Comparative Example 2 performed the worst, with its resistance to ethanol wiping lasting only 24 cycles before the substrate became exposed, and it turned severely white after immersion in water. This is because the PHMG and lignin that have not undergone chemical grafting are water-soluble or hydrophilic and are not locked by a cross-linked network, making them highly susceptible to hygroscopic swelling and even dissolution upon contact with water or polar solvents. In contrast, all examples passed >100 cycles of alcohol wiping and showed no change in water resistance. Example 5 performed particularly well. Although it used a long-chain C16 alkyl group, which theoretically presents the greatest dispersion difficulty, its filtration residue remained very low thanks to the temperature-sensitive shielding technology. At the same time, the strong hydrophobicity of the C16 long chain endowed the coating film with excellent resistance to water whitening.

[0125] Although Comparative Example 3 has a high crosslinking density (alcohol resistance >100 times), it exhibits slight whitening due to the lack of hydrophobic shielding from long-chain alkyl groups. Comparative Example 5 also exhibits slight whitening due to the presence of microscopic voids at the interface between the inorganic filler and the organic matrix, allowing water molecules to easily penetrate along the interface.

[0126] In summary, this invention, through the meticulous design of chemical structures, achieves functionalization without sacrificing the basic protective performance of the coating; on the contrary, it significantly improves upon traditional physical modification methods.

[0127] 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 water-based coating with both sound insulation and antibacterial functions, characterized in that, It is made from the following raw materials in parts by weight: anionic aqueous polyurethane emulsion: 60-90 parts; Multifunctional modified lignin: 10-40 parts; volatile charge shielding agent: 0.5-3.0 parts; water-based additives: 0.1-5.0 parts; deionized water: balance; the multifunctional modified lignin is a lignin derivative grafted with long-chain alkyl groups, hydrophilic polyether segments and cationic guanidine groups, and is prepared by the following method: A1. Dissolve 100g of dried alkali lignin in 300g of dimethyl sulfoxide, heat to 60℃ and stir until completely dissolved, add 0.8g of tetrabutylammonium bromide as a phase transfer catalyst, and add 20g of C12-C14 alkyl glycidyl ether and 10g of methoxy polyethylene glycol glycidyl ether dropwise to the resulting solution, heat to 90℃ and react at a constant temperature for 5 hours to graft long-chain alkyl and hydrophilic polyether segments onto the lignin backbone; A2. Cool the reaction solution obtained in step A1 to 60℃, add 50g of epichlorohydrin, and add dropwise a 20% sodium hydroxide aqueous solution to maintain the pH of the system at 10-11. React for 4 hours. After the reaction is completed, distill under reduced pressure at 60℃ and -0.09MPa for 30 minutes to remove unreacted epichlorohydrin and obtain an intermediate solution containing active epoxy groups. A3. Add 300g of deionized water to the intermediate solution obtained in step A2 for dilution and dispersion, then add 75g of a 40% solid content polyhexamethylene guanidine hydrochloride aqueous solution, adjust the pH of the system to 9.0-9.5, heat to 80℃ and react for 6 hours to allow the amino groups on the polyhexamethylene guanidine hydrochloride to undergo a ring-opening addition reaction with the active epoxy groups. A4. After the reaction is complete, the product solution is placed in a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed in flowing deionized water for 48 hours. The dialyzed solution is then freeze-dried to obtain the multifunctional modified lignin. The preparation of the water-based coating includes the following steps: S1. Disperse the multifunctional modified lignin in deionized water, add the volatile charge shielding agent, control the stirring speed to 300-600 rpm, the stirring time to 30-60 minutes, and adjust the pH value of the premix to 7.8-8.5 to establish ionic equilibrium in the system, thereby obtaining a modified lignin premix with cation shielding. S2. Under shearing and stirring conditions, the modified lignin premix obtained in step S1 is added dropwise to the anionic aqueous polyurethane emulsion to obtain a stable intermediate emulsion. S3. Add the water-based additive to the intermediate emulsion obtained in step S2, adjust the viscosity, filter, and obtain the water-based coating with both sound insulation and antibacterial functions. The volatile charge shielding agent is selected from ammonium carbonate and ammonium bicarbonate.

2. The water-based coating with both sound insulation and antibacterial functions according to claim 1, characterized in that: The hydrophilic polyether segments are derived from epoxy-based polyethylene glycol with a number-average molecular weight (Mn) of 600-2000.

3. The water-based coating with both sound insulation and antibacterial functions according to claim 1, characterized in that: The aqueous additives include film-forming aids, wetting and leveling agents, and defoamers, wherein the film-forming aids are selected from dipropylene glycol butyl ether, dipropylene glycol methyl ether, or dodecyl alcohol ester.

4. The water-based coating with both sound insulation and antibacterial functions according to claim 1, characterized in that: The anionic waterborne polyurethane emulsion has a solid content of 35-50%, and the finished coating has a pH value of 7.5-9.

0.

5. A water-based coating with both sound insulation and antibacterial functions according to claim 1, characterized in that: The specific implementation method of step S2 is as follows: place the anionic aqueous polyurethane emulsion in a dispersion vessel, set the rotation speed to 800-1200 rpm, and add the modified lignin premix at a rate of 5-10 parts / minute, keeping the system in a bluish emulsion state during the addition process.

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