A breathable elastic water-based paint and a preparation method and use method thereof

Abstract

The application discloses a breathable and elastic water-based paint, a preparation method thereof and a use method on living trees or ancient building wooden components. At present, the existing protective coatings have defects such as compactness, poor breathability, poor elasticity, toxic additives and the like, and cannot simultaneously meet the requirements of tree breathability, flexibility, growth adaptation and ecological safety. The water-based paint is prepared from hydrophilic-hydrophobic block modified water-based polyurethane and water-based acrylic emulsion as a film-forming base material to form a high-elasticity interpenetrating polymer network structure (IPN); modified bark micro-powder and diatomite micro-powder are used as fillers to build through channels in the paint film, and the surface hydrophobic interface is formed by directional arrangement of the hydrophobic chain segments to realize water resistance and breathability. The paint film can synchronously stretch and shrink with the deformation of the tree growth, and outdoor gradual degradation is realized through point-like weak bonding and porous structure. The preparation method adopts a pre-closed and pore-forming double insurance process to effectively protect the filler channels from being invaded by the resin. The water-based paint is ecological and non-toxic, and has the dual functions of long-acting protection and healthy growth of trees.

Description

Technical Field

[0001] This invention relates to the field of protective coatings, and more specifically, to a breathable and elastic water-based paint, its preparation method, and its application on living trees or ancient wooden building components. Background Technology

[0002] Currently, protective materials for trees, natural wood, and ancient building timber are mainly divided into three categories:

[0003] 1. Traditional oil-based protective paint: It uses organic solvents as the dispersion medium and contains VOCs, benzene compounds, heavy metals and irritating additives. Although it is waterproof, wear-resistant and has strong adhesion, when used on living ancient trees, it will completely block the bark pores, block the tree's respiration, transpiration and nutrient transport, leading to bark necrosis and tree decline. At the same time, it pollutes the soil and environment, which does not meet the requirements of ecological protection. When used on old wood in ancient buildings, it is easy to yellow and bleed, and damage the original wood texture.

[0004] 2. Ordinary industrial water-based wood coatings: Although they use water as a dispersion medium and are more environmentally friendly than oil-based coatings, their core design is to form a tightly sealed film with high hardness and strong adhesion. The coating film has no breathable structure, poor elasticity, and low elongation at break. When used on ancient trees, they will also cause "suffocating damage." When used on old trees or ancient buildings, they cannot adapt to the thermal expansion and contraction and dry and wet deformation of wood. In a short period of time, the coating film will crack, peel, and fall off, losing its protective effect. Moreover, the formula contains industrial bactericides and amine neutralizers, which will cause bark damage when in contact with living plants, making them unsuitable for the protection of living vegetation.

[0005] 3. Conventional tree whitewash protectants: can only achieve basic frost and insect protection, have no long-lasting waterproofing, extremely poor weather resistance, quickly lose their effectiveness after being washed away by rain, require frequent reapplication, and have no flexible film-forming properties, cannot adapt to tree growth and deformation, and have no long-term protective value. Summary of the Invention

[0006] It is evident that existing technologies cannot meet the protection needs of trees, natural wood, and ancient building timber in terms of breathability, flexibility, environmental safety, and other aspects.

[0007] To address the technical problems existing in the prior art, the present invention provides a waterborne paint comprising a film-forming substrate and a waterborne filler; the film-forming substrate comprises a modified waterborne polyurethane emulsion and a waterborne acrylic emulsion, wherein the modified waterborne polyurethane emulsion is a hydrophilic-hydrophobic block modified waterborne polyurethane with a particle size D50 of 50–150 nm, and the waterborne acrylic emulsion has a particle size D50 of 80–150 nm, and the two can form an elastic film with an interpenetrating polymer network (IPN) together with the hydrophilic-hydrophobic block modified waterborne polyurethane.

[0008] The hydrophilic-hydrophobic block-modified waterborne polyurethane has a soft segment content of 55%-95% and a hard segment content of 5%-45%. The hydrophobic and hydrophilic segments are introduced through block copolymerization, with the hydrophobic segment accounting for 15%-35% by mass. The waterborne filler includes modified bark powder and diatomaceous earth powder. The modified bark powder has a particle size D50 ranging from 5 micrometers to 20 micrometers, an aspect ratio of not less than 2, and a BET nitrogen adsorption specific surface area of ​​not less than 10 m² / g. The diatomaceous earth powder has a particle size D50 ranging from less than 10 micrometers, a micropore size of 100 nm to 500 nm, and a BET nitrogen adsorption specific surface area of ​​not less than 5 m² / g.

[0009] Using hydrophilic-hydrophobic block-modified waterborne polyurethane and waterborne acrylic emulsion as film-forming substrates, the two resin particles can form a highly elastic interpenetrating polymer network (IPN) structure during water evaporation. In this IPN structure, the molecular chains are mainly composed of flexible long-chain segments with coiled conformations and entanglement. This structure gives the coating film low modulus and high elastic recovery characteristics, enabling it to synchronously and reversibly expand and contract with the radial thickening growth of trees and the dimensional changes caused by the dryness and wetness of the xylem and temperature differences, thus inhibiting cracking and peeling of the coating film at the microscale. Modified bark powder and diatomaceous earth powder are uniformly dispersed in the above coating film system. During the film-forming process, the porous powder particles overlap with each other, constructing channels inside the coating film.

[0010] The hard segments in the film-forming substrate aggregate to form physical cross-linking zones, which bond with the plant bark and xylem surfaces through discontinuous point contact, resulting in a coating film with relatively weak interfacial adhesion. This structure, combined with its internal porous structure, allows the coating to gradually and slowly degrade in outdoor environments, thus avoiding physical confinement to tree growth.

[0011] After the paint film cures, it forms a hydrophobic interface on the air interface side through the directional arrangement of hydrophobic segments, so that the static water contact angle after film formation is greater than or equal to 90°. This selective microstructure can effectively block the intrusion of rainwater and liquid water, while allowing water vapor and gas molecules released from the tree bark to be freely transported through the pores, thereby maintaining normal gas exchange in the bark and ensuring the survival of the tree.

[0012] Preferably, the volume ratio of modified waterborne polyurethane emulsion to waterborne acrylic emulsion is 1:0.5–1.2; the mass ratio of diatomaceous earth micropowder to modified bark micropowder is 1.5–2.5:1; and the ratio of the total solid mass of the waterborne filler to the film-forming substrate is 0.4–0.7:1.

[0013] This invention also provides a particularly effective method for preparing the aforementioned waterborne paint, comprising the following steps: Step 1: Dissolve a dispersant in a portion of deionized water, add diatomaceous earth micropowder and disperse evenly, then add a pre-sealed modified bark micropowder paste, stir and mix to obtain a filler pre-dispersion slurry; Step 2: Mix a hydrophilic-hydrophobic block modified waterborne polyurethane emulsion with a waterborne acrylic emulsion, stir, and obtain a film-forming base premix; Step 3: Under stirring conditions, add the filler pre-dispersion slurry obtained in step 1 to the film-forming base premix obtained in step 2, mix evenly, then add a pore-forming agent solution, and continue stirring; Step 4: Add a film-forming aid, a mildew inhibitor, a UV absorber, and a defoamer in sequence, stir and mix; adjust the pH to 7.0–8.0, add a thickener to adjust the viscosity; filter to obtain the waterborne paint.

[0014] In step 1, the pores in the modified bark powder are sealed to prevent resin penetration. In step 3, the pore-forming agent will precipitate upon contact with water after the paint film has cured, releasing the pre-sealing agent along with it. Directly mixing the modified bark powder with the resin emulsion can lead to partial blockage of internal pores, limiting the technical effectiveness to some extent. Adding pre-sealing and pore-forming agents at appropriate times during preparation to treat the water-based filler can better protect the pores and achieve better air permeability.

[0015] Preferably, the modified bark powder paste obtained in step 1 is prepared by the following method: the modified bark powder and the pre-sealing agent are kneaded and impregnated as a protective medium, so that the pre-sealing agent fully occupies the internal pores of the powder, and then excess free liquid is removed to obtain the modified bark powder paste.

[0016] Preferably, the pre-sealing agent is one of polyethylene glycol (PEG)-400, glycerin, aqueous silicone oil, and chitosan solution, and the amount of pre-sealing agent is 0.4–0.8 times the mass of the modified bark powder.

[0017] Preferably, in step 4, the film-forming aid is pinoresinol; the mildew inhibitor is chitosan; the UV absorber is a plant-based UV absorber; the thickener is xanthan gum; and the pH adjuster is sodium bicarbonate. The main components of the water-based paint protected by this invention are free of harmful substances. With the appropriate addition of other plant-derived functional additives, film-forming aids, and mildew inhibitors from existing technologies, the water-based paint of this invention can ensure the safety of plants and the ecological environment throughout the entire process.

[0018] Preferably, the preparation of the modified bark powder specifically includes the following steps: Step 1 - Raw material pretreatment: Select bark with high lignin content and loose structure as raw material, wash and dry it, then pulverize it and pass it through a 40-80 mesh sieve to obtain coarse bark powder; Step 2 - Alkali solution loosening: Treat the coarse bark powder with NaOH alkaline solution, stir and react thoroughly at 80-160℃, wash it with water until neutral, and then dry it until the moisture content is less than 10%; Step 3 - One-time wet grinding: Add the alkali-treated powder and grinding media to a stirring mill. Add a pre-sealing agent to adjust the solid content to 30%-40%, and grind to a particle size of 30-50 micrometers; Step 4 - Surface grafting modification: Disperse the powder after the first grinding in a silane coupling agent solution, stir to react, wash, filter and dry; Step 5 - Secondary wet grinding: Put the modified powder into a grinder, add a pre-sealing agent to adjust the solid content to 20%-30%, grind to a particle size D50 of 5-20 micrometers, separate the solid and liquid to remove the free pre-sealing agent, and then store the modified bark micro powder paste in a moisture-proof manner.

[0019] This invention also provides a method for using the aforementioned water-based paint, comprising the following steps: Step 1: Remove dust, lichen, and moss from the crevices of trees, natural wood, or ancient building timber, without damaging the bark; Step 2: Gently stir the paint; Step 3: Dip the paint into the surface and quickly apply a thin layer along the bark grain to form an extremely thin, semi-transparent primer layer; Step 4: After the first coat is surface dry, apply a second coat in the same direction to form a continuous and uniform thin paint layer; Step 5: The paint film is absolutely waterproof for one day after application and fully cures in 7-14 days; Step 6: Repeat steps 1-5 on the trees every 1-2 years.

[0020] Preferably, the final dry film thickness after curing in step 5 does not exceed 200 micrometers.

[0021] Beneficial effects

[0022] This invention uses hydrophilic-hydrophobic block-modified waterborne polyurethane and acrylic emulsion as the base material to form a highly elastic IPN structure. Combined with modified bark and diatomaceous earth micropowder to construct internal channels and a hydrophobic surface interface, the paint film can expand and contract synchronously with the tree's deformation, preventing cracking while simultaneously blocking water and allowing for air permeability, ensuring the tree's normal respiration. Furthermore, the waterborne paint adheres to the tree surface through dot-like weak adhesion, and combined with the porous structure, the coating can slowly degrade outdoors, avoiding physical confinement to tree growth. Secondly, the main components of the waterborne paint of this invention are non-toxic and harmless, and when used with plant-derived additives, it ensures the safety of plants and the ecological environment. Correspondingly, the preparation method provided by this invention effectively prevents resin penetration into the pores of the bark micropowder, and when used with a pore-forming agent in the waterborne paint, it can significantly improve the air permeability of the paint film during curing and service. Detailed Implementation

[0023] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0024] Preparation example:

[0025] Preparation Example 1: Preparation of Modified Bark Micropowder (Pre-sealed)

[0026] In this preparation example, the bark was wet-milled. PEG-400 was used as a pre-sealing agent and protective medium to seal and protect the pores of the bark microparticles. The specific steps are as follows:

[0027] Step 1: Raw material processing

[0028] Select cedar bark with high lignin content and loose structure. Remove impurities such as soil and moss, wash with water, and dry thoroughly at 60-80℃. Use a plant pulverizer to initially pulverize the bark and pass it through a 40-80 mesh standard sieve to obtain coarse powder with uniform particle size.

[0029] In other embodiments, bark with high lignin content and relatively loose structure, such as cork oak and pine bark, can also be used as raw materials for this invention.

[0030] Step 2: Alkali solution loosening pretreatment

[0031] Prepare a NaOH solution with a concentration of 2-20 g / L. Add the coarse bark powder to the alkali solution at a solid-liquid ratio of 1:10 and stir at 80-160℃ for 1-6 hours. After treatment, thoroughly wash the powder with plenty of water until neutral, and dry at 60-80℃ until the moisture content is below 10%. The low-concentration alkali can hydrolyze some of the hemicellulose and pectin binding the fiber cells, acting as a "chemical loosening" process, while the lignin and cellulose that form the framework are preserved. This step, through chemical methods, "cleans" away some of the substances clogging the natural pores, thus preserving and optimizing the microporous structure.

[0032] Step 3: First wet grinding

[0033] Alkali-treated bark powder and grinding media are added to the grinding chamber of a stirred mill at a volume ratio of 1:5 to 1:10. PEG-400 is added as a pre-sealing agent and protective medium to maintain the slurry solids content at 30-40%. The stirred mill is set to 400-800 rpm and ground for 2-6 hours until the particle size is approximately 30-50 μm. Wet milling can more evenly peel and tear fibers, preserving their sheet-like / fibrous morphology (length-to-diameter ratio greater than 2:1).

[0034] In other embodiments, materials such as glycerol, aqueous silicone oil, and chitosan solution can replace PEG-400 as pre-sealing agents and wet milling protective media.

[0035] Step 4: Surface activation and grafting modification

[0036] The powder was dispersed in a 1-2% aqueous solution of silane coupling agent (KH-550 was used in this example) and stirred for 1-2 hours. The silane coupling agent reacts with the hydroxyl groups on the surface of the plant fibers, forming a coating on the pore walls and stabilizing the microstructure. The powder was then washed, filtered, and dried again to remove unreacted reagents. Chemical modification of the powder after primary grinding stabilized the pore walls and improved its compatibility with the resin.

[0037] Step 5: Second wet grinding

[0038] The modified powder is fed into a grinder, and PEG-400 is added to control the solid content at 20-30%. Grinding is carried out for 1-3 hours. After grinding, excess free PEG-400 is removed by solid-liquid separation. The resulting filter cake is the pre-sealed modified bark micro-powder paste.

[0039] Five 2g paste samples were obtained. Referring to GB / T 19587, the BET specific surface area ranged from 3m² / g to 8m² / g, with an average of 5.2m² / g. Another five 2g paste samples, after washing to remove PEG-400 and drying, showed a BET specific surface area range of 15m² / g to 23m² / g, with an average of 17.8m² / g. This indicates a decrease in BET specific surface area after the pores were sealed. Particle size analysis determined the D50 particle size range to be 5-20μm, with an average of 12.5μm. SEM observation revealed a regular fiber / sheet morphology with an aspect ratio greater than 2:1 (average 3.5), and open micropores were visible on the surface and cross-section.

[0040] Step 6: Preserve the filtered product and seal the sealed bark powder paste in a moisture-proof container. It can be stored stably for 30 days at 5–35℃. When using, add the product directly in paste form.

[0041] Preparation Example 2: Preparation of Modified Bark Micropowder (Unsealed)

[0042] The difference between Preparation Example 2 and Preparation Example 1 is that in step 3 (first wet milling) and step 5 (second wet milling), the pre-sealing agent PEG-400 was replaced with an equal amount of water as the milling protective medium, and after final vacuum drying, unsealed modified bark powder was obtained.

[0043] Five 2g samples were obtained for testing. The BET specific surface area ranged from 15m² / g to 22m² / g, with an average of 17.5m² / g. This indicates no significant difference in pore openness compared to the micropowder obtained after PEG-400 protected grinding. Particle size analysis determined the D50 particle size range to be 5-22μm, with an average of 13.7μm. SEM observation revealed a regular fibrous / sheet-like morphology with an aspect ratio greater than 2:1 (average 3.2). Open micropores were visible on the surface and cross-section, but some areas showed collapse.

[0044] Preparation Example 3: Preparation of Bark Powder (Unmodified)

[0045] The difference between Preparation Example 3 and Preparation Example 2 is that this preparation example does not have step 4 (surface activation and grafting modification).

[0046] Five 2g samples were obtained for testing. The BET specific surface area ranged from 3m² / g to 10.5m² / g, with an average of 6.2m² / g. Particle size analysis determined the D50 particle size range to be 13-36μm, with an average of 18.2μm. SEM observation revealed that the microstructure consisted mostly of near-spherical debris, with few intact fibers, minimal micropores, and an average aspect ratio of 1.5.

[0047] Preparation of diatomaceous earth micro powder:

[0048] The raw diatomaceous earth ore was hydraulically classified to remove impurities, and then calcined at 350℃ for 1.5 hours to remove organic matter without damaging the pores. After air jet milling, it was passed through a 300-mesh sieve, and particles with a D50 of less than 10 μm were collected. Sampling and testing showed that the BET specific surface area of ​​diatomaceous earth micropowder of this particle size was not less than 5 m² / g, and the micropore size was in the range of 100–500 nm.

[0049] Example:

[0050] The following methods were used to set up and employ Examples 1, 2, and Comparative Examples 1-9:

[0051] Example 1: Preparation of water-based paint:

[0052] Step 1: Add 3g of dispersant to 140ml of 70% deionized water and stir at 300rpm for 5min to dissolve; add 120g of diatomaceous earth powder and disperse at 800rpm for 15min. Slowly add 90g of the modified bark powder paste (after sealing treatment) obtained in Preparation Example 1 to the above dispersion and stir at 600rpm for 10min until well mixed.

[0053] Step 2: Add 250 ml of hydrophilic-hydrophobic block modified waterborne polyurethane emulsion (purchased from Bayer U54, particle size D50=50–150 nm, solid content 30% to 35%, anionic, soft segment content 60–70%) and 200 ml of waterborne acrylic emulsion (purchased from BASF Acronal S400F, particle size D50=80–150 nm, solid content 40–45%, Tg=–15℃ to 5℃) to the reactor in proportion, and stir at low speed of 500 rpm for 10 min.

[0054] Step 3: Slowly add the filler dispersion dropwise to the emulsion mixture while stirring at 600 rpm during the dropwise addition process; continue stirring for 15 minutes after the dropwise addition is complete. Then slowly add 25 ml of 40% PEG-2000 aqueous solution at 80℃ (as a pore-forming agent) and stir for 15 minutes until homogeneous.

[0055] Step 4: Add 3g of defoamer (water-based mineral oil) and 20g of rosinol (water-based film-forming aid) in sequence, and stir at 500rpm for 10min; adjust the pH to 7.5 with sodium bicarbonate, and premix 2g of xanthan gum with the remaining 60g of deionized water to form a glue solution, then slowly add the xanthan gum to adjust the viscosity. The finished water-based paint is obtained.

[0056] In other feasible formulations, the volume ratio of modified waterborne polyurethane emulsion to waterborne acrylic emulsion is 1:0.5–1.2; the mass ratio of diatomaceous earth micropowder to modified bark micropowder (pure dry powder) is 1.5–2.5:1; and the ratio of total filler mass (diatomaceous earth + bark powder) to total emulsion solid mass is 0.4–0.7:1. The amount of pre-sealing agent is 0.4–0.8 times the mass of modified bark micropowder; and the amount of pore-forming agent accounts for 0.5–2% of the total solid mass of the formulation.

[0057] The soft segments of hydrophilic-hydrophobic block-modified waterborne polyurethane provide the flexibility and elasticity of the coating film, and are also fundamental to key properties such as hydrolysis resistance. To ensure breathability and prevent liquid water penetration, the soft segment content is typically 55%-95%. The hard segments aggregate through strong hydrogen bonding to form physical cross-linking points, anchoring the flexible soft segment network. The hard segment content is typically 5%-45%, and increasing its content can improve the film strength, hardness, and heat resistance. In other feasible formulations, soft segment contents ranging from 55-70%, 60-75%, and 75-95% all achieve the desired results.

[0058] In other feasible formulations, the hydrophilic-hydrophobic block-modified waterborne polyurethane can be selected from products of other chemical suppliers. However, the hydrophobic and hydrophilic segments must be introduced via block copolymerization, for example, in an ABA or AB manner. The hydrophobic segments can be selected from at least one of fluorinated segments, silicone segments, or long-chain alkyl segments, and a mass fraction of 15%–35% can ensure a static water contact angle after film formation.

[0059] Example 1: Application of water-based paint:

[0060] The water-based paint was applied to a natural wood sample board or natural tree using the following method: Dust was removed from crevices, taking care not to damage the bark; the water-based paint obtained in Example 1 was gently stirred; the paint was applied quickly and thinly along the bark grain to form an extremely thin, translucent primer layer; after the first coat was surface dry, a second coat was applied in the same direction to form a continuous, uniform thin paint layer. The paint film is absolutely waterproof for one day after application and fully cures in 7-14 days. Testing showed that the dry film after two coats was relatively thin, ranging from 120 to 200 micrometers (if three or more coats are applied, the dry film thickness will exceed 250 micrometers, which will significantly affect breathability).

[0061] Example 2: Preparation and use of water-based paint: The difference between Example 2 and Example 1 is that in step 1, 90g of modified bark micropowder (without pre-sealing treatment) prepared in Example 2 is added, and in step 3, 25ml of PEG-2000 aqueous solution is replaced with an equal amount of deionized water to obtain the finished water-based paint.

[0062] Compare with Example 1: The difference from Example 1 is that 90g of unmodified and pre-sealed bark powder prepared in Preparation Example 3 was added in step 1, and 25ml of PEG-2000 aqueous solution was replaced with an equal amount of deionized water in step 3.

[0063] Compare with Example 2: The difference from Example 1 is that only 450 ml of hydrophilic-hydrophobic block modified waterborne polyurethane emulsion was used in step 2, and waterborne acrylic emulsion was not used.

[0064] Compare with Example 3: The difference from Example 1 is that only 450 ml of aqueous acrylic emulsion was used in step 2, and aqueous polyurethane emulsion was not used.

[0065] Compare with Example 4: The difference from Example 1 is that in step 2, 250 ml of aqueous anionic polyurethane dispersion (YX-T52, purchased from Shanghai SHARK) was mixed with 200 ml of aqueous acrylic emulsion.

[0066] Compare with Example 5:The difference from Example 1 is that in step 1, 210g of modified bark micropowder paste was added to the dispersion, instead of adding diatomaceous earth micropowder.

[0067] Compare with Example 6: The difference from Example 1 is that in step 1, 210g of diatomaceous earth powder was added to the dispersion, instead of modified bark powder.

[0068] Compare with Example 7: The difference from Example 1 is that no filler is added in step 1 (neither the modified bark micro powder filter cake nor the diatomaceous earth micro powder is added), and the dispersant is dissolved in deionized water and then directly combined with the emulsion mixture in step 2.

[0069] Control group 8: The difference from Example 1 is that when applying the water-based paint of Example 1 to the sample plate, three layers were applied, and the dry film after curing was approximately 288 micrometers.

[0070] Control group 9: Commercially available whitewash for common trees (the whitewash was purchased from Piaolv Group's Piaolv Qingyuan powder).

[0071] Performance testing

[0072] I. Thermal properties (DSC measurement of Tg)

[0073] Following ISO 11357-2, 5–10 mg of cured paint film was taken, heated to 120 °C to eliminate thermal history, quenched to -80 °C, and then heated again to 120 °C at a rate of 20 °C / min. The glass transition step was recorded within the 10–30 °C range using the midpoint method to determine the glass transition temperature (Tg). This was to verify the formation of the IPN interpenetrating structure and the amorphous structure of the paint film.

[0074]

[0075] DSC test results verified the structure of the present invention: In Example 1, the soft segment phase of the block-modified polyurethane had a Tg as low as -47°C, providing a highly elastic basis for the coating film; the acrylic phase and the hard segment of polyurethane fused in the 10–30°C range to form a single broadened Tg (18.5°C), and there was no crystallization melting peak throughout the entire temperature range. This conclusively proves the successful construction of the IPN interpenetrating network at the molecular level and the completely amorphous characteristics of the coating. In contrast, neither polyurethane (Comparative Example 2) nor acrylic (Comparative Example 3) alone could form an IPN mixed phase, while the system using ordinary linear polyurethane (Comparative Example 4) showed obvious phase separation and the Tg failed to fuse, confirming the necessity of the hydrophilic-hydrophobic block structure for realizing IPN.

[0076] II. Mechanical and Elastic Properties

[0077] 1. Tensile modulus: Referring to GB / T1040.3, cut the cured paint film into dumbbell-shaped specimens with a gauge length of 25 mm and a tensile speed of 50 mm / min. Take the initial linear segment of the stress-strain curve and calculate the slope, which is the tensile modulus (MPa). Test 5 specimens and take the average value.

[0078] 2. Elongation at break: Same as GB / T1040.3, using dumbbell-shaped specimens, gauge length 25 mm, tensile speed 50 mm / min. Record the displacement between gauge lengths when the specimen breaks. Elongation at break = displacement / 25 mm × 100%. Take the average value of 5 specimens.

[0079] 3.50% elastic recovery rate: Referring to the principle of GB / T528, a dumbbell-shaped specimen is stretched to 50% strain at 50 mm / min and held for 1 min, then unloaded to zero stress at the same speed. The residual strain is recorded. Elastic recovery rate = (50% – residual strain) / 50% × 100%;

[0080] 4.50% strain cyclic stretching 100 times: Referring to the principle of ISO 6943, set the cycle program: stretch to 50% strain at 100 mm / min and then return at the same speed, repeat 100 times. Take the data at the 1st, 10th, 50th and 100th cycles and record the cumulative value of residual strain.

[0081]

[0082] The coating without any fillers (Comparative Example 7) exhibited significantly inferior overall mechanical properties compared to Example 1, which included modified bark powder and diatomaceous earth powder. This is because the film-forming matrix of this invention is specially designed with a low intrinsic modulus. Without fillers, the pure resin film is prone to molecular chain slippage under external force, leading to linear crack propagation, resulting in an elongation at break of only 120% and a cyclic tensile residual strain of 15.6%. In contrast, Example 1 showed an elongation at break of 280% and a cyclic residual strain of only 3.2%, possibly due to the interconnected microporous network formed by the overlapping of the two powders acting as a microscopic "deformation buffer," allowing localized stress release without triggering macroscopic cracking.

[0083] III. Air permeability and water resistance

[0084] 1. Static water contact angle: Refer to GB / T30693-2014 "Measurement of contact angle between plastic film and water". Using a contact angle meter, add 5μL of deionized water to the air side surface of the coating film at 25℃, and measure the tangent angle at the gas-liquid-solid three-phase interface within 10 seconds. Average the 5 points. A value greater than 95° indicates hydrophobicity.

[0085] 2. Initial water vapor transmission rate: Refer to GB / T1037-2021 "Determination of Water Vapor Transmission Performance of Plastic Films and Sheets - Cup Method for Weight Gain and Loss". Seal the free paint film on a permeation cup containing desiccant and place it in an environment of 38±0.5℃ and 90±2%RH. Under the water vapor pressure difference on both sides, gas molecules are absorbed by the desiccant through the paint film. Weigh the film periodically until a stable weight gain is achieved. Calculate: Transmission rate (g / (m²·24h)) = (Δm) / (Δt×A).

[0086] 3. Improvement in water vapor transmission rate after immersion: Refer to the cup method in GB / T1037-2021. Immerse the paint film in deionized water at 25℃ for 7 days, then remove and dry at 25℃ for 24 hours. Measure the water vapor transmission rate after immersion using the same cup method as above. Calculate the improvement rate of air permeability after immersion. This index quantifies the dynamic improvement effect of newly formed interconnected micropores on air permeability after the pore-forming agent dissolves.

[0087]

[0088] The air permeability and water resistance performance testing system verified the successful implementation of the dual mechanism of air permeability and dynamic pore formation in this invention. In Example 1, the static water contact angle was 102°, the initial water vapor transmission rate was 105 g / (m²·24h), and after 7 days of immersion, the air permeability increased by 32%, with all three indicators significantly better than all control examples. Data comparison revealed that Examples 2 and Control Example 4, due to the lack of pore-forming agents or block structures, only showed an improvement of 5%–18% after immersion.

[0089] The initial water vapor transmission rate of Comparative Example 2 (98 g / (m²·24h)) was close to that of Example 1 (105). However, this is due to the essential difference in their permeability mechanisms: Comparative Example 2 is a pure polyurethane system without acrylic acid phase restriction, and the continuous molecular-level diffusion channels of the PU soft segments are more unobstructed. In contrast, the permeability of pure acrylic acid in Comparative Example 3 is only 28%, and the permeability of the unfilled mixed resin system in Comparative Example 7 is only 35%. It can be seen that although molecular diffusion in Example 1 is slightly hindered by the acrylic acid phase in IPN, it has filler-through channels that Comparative Example 2 does not have, which can carry out efficient gas convection transport, proving that porous powder is the main permeability channel.

[0090] The above results demonstrate that the present invention, through the synergistic strategy of pre-sealing, dynamic release of pore-forming agent, and hydrophobic interface, successfully achieves adaptive growth of coating permeability over service time, fundamentally solving the problem that dense water-based paint films may cause trees to suffocate.

[0091] IV. Adhesion State and Degradability

[0092] 1. Pull-out adhesion strength (bark substrate): Refer to GB / T5210-2006 "Paints and Varnishes - Pull-out Adhesion Test". A test column is bonded to a coating on the surface of natural bark. After curing, it is pulled out at a uniform speed of 0.2 MPa / s until failure, and the failure stress (MPa) is recorded. The average of 5 groups is taken.

[0093] 2. SEM observation of the peeling interface: After the pull-out test, the peeling interface is sputter-coated with gold and the morphology of the damage is observed using a scanning electron microscope at 500–2000x magnification. If the resin remains as discrete islands rather than continuous film tears, it is determined to be point adhesion.

[0094] 3. Mass loss rate after 6 months of soil burial: A coated test panel with a known mass (m0) was buried 20cm deep in natural soil. After 6 months, it was removed, cleaned, dried, and weighed (m1). Mass loss rate = (m0 – m1) / m0 × 100%. The average of 5 groups was taken.

[0095] 4. Adhesion (Cross-cut Test): Refer to GB / T9286-2021 "Cross-cut Test for Paints and Varnishes". Draw a 6×6 grid (2mm spacing) on ​​the coating, stick it with tape, and then peel it off. Rate it according to the six-level standard (0B–5B). Take the average of 5 groups.

[0096] 5. Coating appearance (6 months after burial): Visually inspect the coating surface after 3 months of burial using a 10x magnifying glass to check for blistering, cracking, peeling, and traces of microbial erosion, and record the uniformity of degradation.

[0097]

[0098] Example 1 showed a pull-out bond strength of only 0.18 MPa, with SEM confirming point-like adhesion at the peel interface and a cross-cut adhesion of 3B. Furthermore, after 6 months of soil burial, the weight loss rate reached 22%, indicating uniform microporous degradation of the paint film. In contrast, the pure acrylic system (Control Example 3) exhibited a high bond strength of 0.35 MPa, an adhesion of 1B, and a loss rate of only 5%, demonstrating strong adhesion and resistance to degradation. The filler-free system (Control Example 7) showed a bond strength of 0.45 MPa and a loss rate of only 3%, with a dense and intact film. The diatomaceous earth-only system (Control Example 6) had a loss rate of only 8% and lacked biodegradation initiation points from bark powder. The commercially available whitewash (Control Group 9) showed a bond strength of only 0.05 MPa, significant physical loss, and no long-term protective capability.

[0099] V. Coating Test on Live Trees

[0100] 1. Simulated Tree Trunk Radial Growth Test: A paint film was coated onto the surface of a superabsorbent resin rod, and the amount of water absorption and expansion of the substrate was controlled to simulate the annual radial growth of a tree trunk by 5%. Ten cycles of expansion and contraction were performed, and the paint film was visually inspected and examined under a 50x microscope for cracking and peeling. No cracks were expected after the cycles.

[0101] 2. Temperature and humidity cycling test: Refer to JG / T25-2017 "Test Method for Temperature Deterioration Resistance of Architectural Coatings". Place the coating test panel in a temperature and humidity alternating test chamber, maintain a constant temperature of -20℃ for 3 hours, then raise the temperature to 60℃ and maintain a constant temperature of 90%RH for 3 hours as one cycle, with a transition time ≤30 minutes, and repeat 50 times. Visually inspect the coating for blistering, cracking, peeling, and discoloration.

[0102] 3. VOC content: Refer to GB / T23986-2009 "Determination of Volatile Organic Compounds (VOCs) in Paints and Varnishes - Gas Chromatography". Weigh approximately 1g of liquid paint sample, dilute with solvent, and analyze using a gas chromatograph. Use the internal standard method or external standard method for qualitative and quantitative analysis of each compound. Calculate the VOC content (g / L) after deducting water content.

[0103] 4. Diameter at breast height (DBH) growth of trees one year after coating: Five living poplar trees of the same age and species with uniform growth vigor were selected. A 50cm long area at DBH was marked on each tree and coated with the coating. Adjacent areas served as blank controls. Before coating, the initial DBH of the coated and control areas was measured using a tree measuring tape. The same location was measured again one year after coating. DBH growth = DBH after one year – initial DBH. The ratio of growth in the coated area to the control area was used to evaluate the effect of the coating on tree growth.

[0104]

[0105] Example 1 showed no cracking or warping during 10 cycles simulating 5% annual radial growth, and no degradation after 50 temperature and humidity shocks from -20℃ to 60℃. The VOC content was only 18 g / L, and after one year, the tree's diameter at breast height (DBH) growth reached 97% of the control group. Comparative data clearly revealed that the pure acrylic system (Control Example 3) cracked after the second treatment, with a growth inhibition rate of 22%; the filler-free system (Control Example 7) cracked after the sixth treatment, with a growth rate of only 91%; excessively thick coatings (Control Group 8) significantly deteriorated both mechanical and air permeability; commercially available whitewash (Control Group 9) completely lacked elasticity and weather resistance, and due to alkaline stress, the tree's growth was only 85%. These results conclusively confirm that the present invention, through the synergy of the IPN high-elasticity network, porous filler stress buffer, and selective air permeability structure, successfully achieves dynamic synchronous adaptation between the coating and tree growth.

[0106] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A water-based paint, characterized in that, Includes film-forming substrate and aqueous filler; The film-forming substrate comprises a modified aqueous polyurethane emulsion and an aqueous acrylic emulsion, wherein, The modified waterborne polyurethane emulsion is a hydrophilic-hydrophobic block modified waterborne polyurethane with a particle size D50 of 50–150 nm, and the waterborne acrylic emulsion has a particle size D50 of 80–150 nm. They can form an elastic film with an interpenetrating polymer network (IPN) with the hydrophilic-hydrophobic block modified waterborne polyurethane. The hydrophilic-hydrophobic block-modified waterborne polyurethane has a soft segment content of 55%-95% and a hard segment content of 5%-45%. The hydrophobic and hydrophilic segments are introduced by block copolymerization, with the hydrophobic segment accounting for 15%-35% by mass. The aqueous filler comprises modified bark powder and diatomaceous earth powder, wherein, The modified bark powder has a particle size D50 ranging from 5 micrometers to 20 micrometers, a particle aspect ratio of not less than 2, and a BET nitrogen adsorption specific surface area of ​​not less than 10 m² / g. The diatomaceous earth micropowder has a particle size D50 of less than 10 micrometers, a micropore size of 100nm to 500nm, and a BET nitrogen adsorption specific surface area of ​​not less than 5m² / g.

2. The water-based paint as described in claim 1, characterized in that, The volume ratio of modified waterborne polyurethane emulsion to waterborne acrylic emulsion is 1:0.5–1.2; the mass ratio of diatomaceous earth micropowder to modified bark micropowder is 1.5–2.5:1; and the mass ratio of the waterborne filler to the total solids of the film-forming substrate is 0.4–0.7:

1.

3. A method for preparing the water-based paint according to claims 1-2, characterized in that, Includes the following steps: Step 1: Dissolve the dispersant in part of the deionized water, add diatomaceous earth powder and disperse evenly, then add the pre-sealed modified bark powder paste, stir and mix to obtain the filler pre-dispersion slurry; Step 2: Mix the hydrophilic-hydrophobic block modified waterborne polyurethane emulsion with the waterborne acrylic emulsion and stir to obtain a film-forming base material premix. Step 3: Under stirring conditions, add the pre-dispersed filler slurry obtained in S1 to the premixed film-forming base material obtained in S2, mix evenly, add the pore-forming agent solution, and continue stirring; Step 4: Add the other functional components of the water-based paint in sequence, adjust the pH to 7.0–8.0, and stir to mix to obtain the water-based paint.

4. The method for preparing water-based paint as described in claim 3, characterized in that, The modified bark powder paste obtained in step 1 is prepared by the following method: the modified bark powder and the pre-sealing agent are kneaded and impregnated as a protective medium, so that the pre-sealing agent fully occupies the internal pores of the powder, and then excess free liquid is removed to obtain the modified bark powder paste.

5. The method for preparing water-based paint as described in claim 4, characterized in that, The pre-sealing agent is one of polyethylene glycol (PEG)-400, glycerin, aqueous silicone oil, and chitosan solution, and the amount of pre-sealing agent is 0.4–0.8 times the mass of the modified bark powder.

6. The method for preparing water-based paint as described in claim 3, characterized in that, In step 3, the pore-forming agent is a water-soluble polymer, which is one of PVA (polyvinyl alcohol), PEG-2000, PEG-4000, PEG-6000, polyvinylpyrrolidone (PVP), starch, dextrin, sodium alginate, and polylactic acid (PLA). The amount of pore-forming agent is 0.5–2% of the total mass of the water-based paint.

7. The method for preparing water-based paint as described in claim 3, characterized in that, The functional components of the water-based paint described in step 4 include film-forming aids, mildew inhibitors, UV absorbers, and defoamers; wherein the film-forming aid is rosinol; the mildew inhibitor is chitosan; the UV absorber is a plant-based UV absorber; and the thickener is xanthan gum.

8. The method for preparing water-based paint as described in claim 4, characterized in that, The preparation of the modified bark powder specifically includes the following steps: Step 1 - Raw material pretreatment: Select bark with high lignin content and loose structure as raw material, wash and dry it, then crush it and pass it through a 40-80 mesh sieve to obtain coarse bark powder; Step 2 - Alkali Solution Loosening: Treat the coarse bark powder with NaOH alkaline solution, stir thoroughly at 80-160℃, wash with water until neutral, and then dry until the moisture content is less than 10%. Step 3 - One-time wet grinding: Add the alkali-treated powder and grinding media to a stirring mill, add a pre-sealing agent to adjust the solid content to 30%-40%, and grind to a particle size of 30-50 micrometers; Step 4 - Surface grafting modification: Disperse the powder after one grinding in a silane coupling agent solution, stir to react, wash, filter and dry; Step 5 - Secondary wet grinding: Put the modified powder into a grinder, add a pre-sealing agent to adjust the solid content to 20%-30%, grind to a particle size D50 of 5-20 micrometers, separate the solid and liquid to remove the free pre-sealing agent, and then store the modified bark micro powder paste in a moisture-proof manner.

9. A method of using the water-based paint according to claims 1-2, characterized in that: Includes the following steps: Step 1: Remove dust, lichen, and moss from the crevices of living trees or wooden components of ancient buildings, without damaging the bark; Step 2: Gently stir the paint; Step 3: Dip the brush in the lacquer and quickly apply a thin layer along the bark texture to form an extremely thin, semi-transparent base coat. Step 4: After the first coat is surface dry, apply the second coat in the same direction to form a continuous and even thin layer of paint. Step 5: The paint film is absolutely waterproof for 1 day after application and fully cured in 7-14 days; Step 6: Repeat steps 1-5 above for the trees every 2 years.

10. The method of using the water-based paint as described in claim 9, characterized in that, The final dry film thickness does not exceed 200 micrometers.

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