Preparation method and application of natural plant dye-based water-based paint

Abstract

The application provides a preparation method and application of a natural plant dye-based water-based paint. The application uses a natural plant dye as a colorant and is compounded with modified silicon dioxide. The modified silicon dioxide takes aminosilica as a core, forms an adsorption active layer through tannic acid grafting, and then is crosslinked and copolymerized with an acrylate monomer through a double bond to form an organic crosslinked layer. Finally, an inorganic core, an adsorption active layer and an organic crosslinked layer are combined to form a structure. The surface has adsorption sites and polymer segments matching the water-based resin system, which can significantly improve the dispersibility, compatibility and adsorption capacity in the paint. When the modified silicon dioxide is used in the natural plant dye-based water-based paint, the dye can be stably dispersed, the color bleeding and floating can be improved, the comprehensive performance of the coating adhesion, hardness, water resistance, solvent resistance and the like can be improved, the paint is environmentally friendly and safe, has excellent protection and decoration effects, and is suitable for coating various substrates.

Description

Technical Field

[0001] This invention relates to the field of water-based coatings technology, specifically to a method for preparing and applying water-based coatings based on natural plant dyes. Background Technology

[0002] Coatings are a type of polymer material frequently used in industrial production and daily life, with extremely large production and consumption volumes. Traditional coatings are mainly based on oil-soluble polymers (such as benzene, toluene, and aldehydes as solvents). While these coatings possess excellent physical and chemical properties, their solvents have high volatility and cause significant environmental pollution, posing a great threat to human health. With increasing global demands for green and environmentally friendly practices, the coatings industry is actively shifting towards development in this field.

[0003] Water-based coatings have been widely used in various surface coating fields due to their advantages such as environmental friendliness, safety, and low VOC emissions. However, the colorants currently used in water-based coatings are mainly synthetic dyes, which have problems such as limited color options and environmental pollution. Furthermore, some synthetic dyes contain harmful substances such as heavy metals, affecting the environmental characteristics of water-based coatings.

[0004] Natural plant dyes are a green and environmentally friendly coloring material with a history of application dating back thousands of years. Traditional delicacies from ethnic minorities in southern my country use natural plant dyes such as maple leaves, red and blue clover, buddleja officinalis, purple clover, and butterfly pea flowers to create five colors: black, red, yellow, purple, and blue. These colors are vibrant, fragrant, and possess medicinal value. This traditional dyeing process utilizes the natural pigments in plants, coloring the substrate through physical adsorption and chemical bonding. Natural dyes offer advantages such as being non-toxic, renewable, possessing unique colors, and rich in bioactive components, giving coatings unique decorative effects and cultural connotations. However, their application in water-based coatings faces challenges such as poor solubility or water dispersibility, low compatibility with water-based systems, and insufficient weather resistance.

[0005] Existing technologies often improve the dispersibility and compatibility of natural dyes through chemical modification. However, this process introduces chemical reagents, compromising the environmentally friendly properties of natural dyes, and often results in poor coating performance due to insufficient compatibility. Therefore, developing a water-based coating made from natural plant dyes that does not require complex modification of natural dyes, can be directly adapted to water-based systems, ensures satisfactory overall coating performance, and combines environmental friendliness and practicality has become an urgent technical problem to be solved in this field.

[0006] In conclusion, a new technical solution is urgently needed to address the problems existing in the current technology. Summary of the Invention

[0007] Based on this, the present invention provides a method for preparing and applying water-based coatings based on natural plant dyes. The present invention uses traditional water extraction or fermentation methods to extract natural dyes from plants such as maple leaves, red and blue grass, buddleja officinalis, purple and blue grass, and butterfly pea flowers. These dyes are then applied to water-based coatings through three methods: direct addition, reduction treatment, or addition after drying. The present invention eliminates the need for complex modification of the natural dyes, resulting in a simple process, good environmental friendliness, and excellent coating performance. Experimental tests show that the water-based coatings prepared by this invention exhibit excellent performance in key indicators such as adhesion, hardness, water resistance, and solvent resistance. They can be widely used in primer, topcoat, and floor coating processes on surfaces such as glass products (e.g., wine bottles), wood, metal, and flooring, demonstrating promising application prospects.

[0008] One object of the present invention is to provide a water-based coating based on natural plant dyes, the water-based coating comprising the following components in parts by weight: 10-20 parts of natural dye dispersion 15-50 parts of water-based resin 2-6 parts of modified silica 0.5-16 parts of auxiliary agent Solvent 20-60 parts; in, The modified silica is obtained by grafting silica with tannic acid to introduce double bonds, followed by copolymerization with pentaerythritol triacrylate and hydroxyacrylate.

[0009] Furthermore, the natural dye dispersion is obtained by extraction and purification from natural plants, including black dye dispersion, red dye dispersion, yellow dye dispersion, purple dye dispersion, and blue dye dispersion; the natural plants are selected from one or more of the following: maple leaves, safflower, sappanwood, buddleja officinalis, gardenia, turmeric, purplish-blue grass, purplish-red-blue grass, butterfly pea flower, storax, polygonum tinctorium, and isatis tinctoria.

[0010] Furthermore, the solid content of the natural dye dispersion is 20%-40%.

[0011] Furthermore, the method for preparing the natural dye dispersion includes: Black dye dispersion: Utilizing tender leaves and bark of the sweetgum tree (maple leaves). Specific steps include (maple leaf method): Take fresh tender leaves and bark of the sweetgum tree, wash and crush them, then soak them in water for 24-72 hours. During soaking, rub the leaves three times daily to promote melanin extraction. The soaking temperature is controlled at 30-40℃, and the water-to-maple leaf mass ratio is 5-10:1. After soaking, remove the residue, aerate or stir for 1-2 hours at a stirring speed of 300-500 rpm, let stand for 12-24 hours, and collect the black dye precipitate at the bottom. The dye solids content is 20%-40%. The extraction process involves no chemical additives and meets the requirements for green coatings.

[0012] Red dye dispersion: Use the stems and leaves of *Sedum sarmentosum* (round leaves) or sappanwood chips. Specific steps include (Sedum sarmentosum method): Method 1: Take fresh stems and leaves of *Sedum sarmentosum* (round leaves), wash and chop them, boil them in water for 10-20 minutes (water to sedum sarmentosum mass ratio 8-15:1), cool and filter to obtain a red dye solution. Method 2: Take sappanwood chips, add water and boil for 12-15 minutes (water to sappanwood mass ratio 10-15:1), filter to obtain an orange-red dye solution.

[0013] Yellow dye dispersion: This is achieved using Buddleja officinalis (yellow rice flower), Gardenia jasminoides fruit, or turmeric tuber. Specific steps include (Buddleja officinalis / Gardenia jasminoides method): Method 1: Take Buddleja officinalis flowers (fresh or dried) or Gardenia jasminoides fruit, crush them, and boil them in water for 15-30 minutes. The mass ratio of water to Buddleja officinalis / Gardenia jasminoides is 8-12:1. Filter to obtain the yellow dye solution. Method 2: Peel turmeric, crush it, and rub it with warm water to extract turmeric juice.

[0014] Purple dye dispersion: The stems and leaves of *Indigofera tinctoria* (long-leaved grass) or *Indigofera tinctoria* are used. Specific steps include (Indigofera tinctoria method): Wash and chop fresh *Indigofera tinctoria* stems and leaves, boil them in water for 15-25 minutes (water to *Indigofera tinctoria* mass ratio 6-10:1), and filter to obtain the purple dye solution; or use *Indigofera tinctoria* and extract using the same method.

[0015] Blue dye dispersion: This is achieved using butterfly pea flowers, or the stems and leaves of traditional indigo plants such as scotch, indigofera, and woad. Specific steps include (Butterfly Pea Flower / Indigo Plant Method): Method 1: Take butterfly pea flowers, boil them in water for 10-20 minutes (water to flower mass ratio 10-15:1), and filter to obtain a blue dye solution. Method 2: Take the stems and leaves of indigo plants such as scotch, indigofera, and woad, and prepare the blue dye using the traditional fermentation method: Soak the indigo plants in water for 3-7 days at 20-40℃ (water to indigo plant mass ratio 5-15:1), add lime to adjust the pH to 6.5-8.5 (lime addition amount 5%-10% of the indigo plant raw material weight); remove the residue, aerate or stir for 1-2 hours, let stand for 4-5 days, and collect the blue dye precipitate at the bottom.

[0016] Furthermore, the waterborne resin is selected from one or more of waterborne acrylic resin, waterborne alkyd resin, waterborne epoxy resin, or waterborne polyurethane resin.

[0017] Furthermore, the additive is selected from one or more of dispersants, defoamers, thickeners, preservatives, and antioxidants.

[0018] Another object of the present invention is to provide a method for preparing the aforementioned water-based coating based on natural plant dyes, comprising the following steps: S1. Aminated silica, tannic acid and glutaraldehyde are mixed and stirred to react, yielding intermediate product 1. S2. The intermediate product 1 is blended with glycidyl methacrylate, and the mixture is heated to react under the action of a catalyst and a polymerization inhibitor to obtain intermediate product 2. S3. The intermediate product 2, pentaerythritol triacrylate and hydroxy acrylate are blended together, an initiator is added, and the mixture is reacted under an inert atmosphere and heating conditions to obtain modified silica. S4. Mix all components thoroughly to obtain a water-based coating based on natural plant dyes.

[0019] Further, in step S1, the mass ratio of the aminated silica, tannic acid and glutaraldehyde is 1:(0.1-0.9):(1-5).

[0020] Further, in step S2, the mass ratio of intermediate product 1 to glycidyl methacrylate is 1:(0.5-1.5).

[0021] Furthermore, in step S2, the heating temperature is 80-100℃.

[0022] Further, in step S3, the mass ratio of intermediate product 2, pentaerythritol triacrylate and hydroxyacrylate is 1:(0.1-0.9):(0.5-2).

[0023] Furthermore, in step S3, the heating temperature is 60-80℃.

[0024] Further, in step S4, all components are mixed evenly by dispersion grinding. The conditions for dispersion grinding are: rotation speed 1000-1500 rpm, time 30-60 min, and particle size ≤30 μm.

[0025] Furthermore, the water-based coating based on natural plant dyes also includes a reduction treatment step: take a natural dye dispersion, add a reducing agent, and stir at 50-60℃ for 20-30 min to carry out reduction treatment to obtain a soluble dye solution; the reducing agent is selected from sodium hydrosulfite or glucose, and the amount added is 0.5%-3% of the mass of the natural dye.

[0026] Furthermore, the water-based coating based on natural plant dyes also includes a dye drying step: drying the natural dye dispersion at 30-60℃ until the moisture content is ≤5%, and pulverizing it to 200-300 mesh to obtain dye powder.

[0027] Another object of the present invention is to provide the application of the aforementioned water-based coatings based on natural plant dyes in the surface coating of glass products, wood, metal or flooring.

[0028] Furthermore, the glass products include wine bottles, glassware, or glass handicrafts.

[0029] Furthermore, the water-based coating based on natural plant dyes can be used as a primer, topcoat, or floor coating.

[0030] Furthermore, the application method of the water-based coating based on natural plant dyes includes spraying, scraping, or brushing, followed by drying at 80-120℃ for 15-30 minutes to form a coating.

[0031] Furthermore, the five-color natural plant dyes used in this invention are rich in various natural bioactive components (such as polyphenols, flavonoids, anthocyanins, etc.). In subsequent applications, the dye sludge can be further mildly biomodified using enzymes or microorganisms, significantly improving its dispersion stability in water-based coatings without introducing chemically synthesized substances. The biomodified dye sludge can more efficiently remove free radicals from the system, thereby giving the coating superior antioxidant properties; at the same time, its interfacial bonding with the matrix resin is enhanced, further improving the coating's weather resistance and yellowing resistance, maintaining color stability under long-term ultraviolet irradiation and harsh environmental conditions, extending the service life of the bottle coating, while maintaining the green and environmentally friendly characteristics of the process. This biomodification extension scheme is only used as a pretreatment extension of the dye raw materials, without changing the main process route of this invention, and seamlessly adapts to the aforementioned three application schemes (direct addition, reduction treatment, and drying addition), which can be selectively implemented according to actual performance requirements.

[0032] The present invention has the following beneficial effects: (1) This invention provides a method for preparing and applying a water-based coating based on natural plant dyes. The water-based coating based on natural plant dyes uses natural plant dyes as coloring materials and incorporates modified silica. First, using aminated silica as the core, a dendritic structure rich in hydroxyl groups is covalently grafted onto the particle surface via tannic acid and glutaraldehyde. Then, double bonds are introduced via glycidyl methacrylate, followed by cross-linking copolymerization with pentaerythritol triacrylate and hydroxy acrylate to form a cross-linked polymer layer on the outside of the active layer. This cross-linked polymer layer contains similar chain segments to the water-based resin and possesses a three-dimensional structure and hydroxyl groups, effectively improving compatibility with the resin while further enhancing the mechanical and adsorption properties of the coating. Finally, a modified silica with a composite structure combining an inorganic core, an adsorption active layer, and an organic cross-linked layer is formed. The surface of this modified silica possesses both active adsorption sites and organic polymer chain segments, effectively improving its adsorption performance, dispersion stability, and interfacial bonding in the water-based coating system.

[0033] This invention incorporates modified silica into water-based coatings based on natural plant dyes. This modified silica utilizes its active adsorption sites to stably anchor and uniformly disperse natural dye molecules, improving the problems of agglomeration, floating color, and color blooming of natural dyes in water-based systems, and enhancing their lightfastness. Simultaneously, relying on the good interfacial compatibility between the organic crosslinking layer and water-based resins, additives, and other components, the overall film-forming properties and mechanical properties of the coating are improved. This enhances the adhesion of the coating to various substrates such as glass, wood, metal, and flooring, and synergistically optimizes the coating's water resistance, solvent resistance, and chemical resistance. The resulting coating achieves a grade 0 adhesion, a pencil hardness of at least 2H, water resistance of at least 240 hours, and alcohol resistance of at least 24 hours. While meeting green environmental protection requirements, it also possesses superior comprehensive protective and decorative properties.

[0034] (2) This invention uses natural plant dyes as colorants and innovatively applies the principle of coloring traditional natural pigments through physical adsorption and chemical bonding to water-based coating systems, effectively broadening the application range of natural dyes. The raw materials used, such as maple leaves, red and blue grass, buddleja flowers, purple grass, and butterfly pea flowers, are all food-grade natural dyes, which are safe and non-toxic and have certain medicinal value. They meet food-grade safety standards and can be used in coating fields with high safety requirements, such as food packaging and wine bottles. At the same time, the coating preparation process is simple and can be applied through three schemes: direct addition, reduction treatment, and drying addition. There is no need for complex equipment and dye modification treatment, which is suitable for industrial production. In addition, the water-based coatings made of natural plant dyes prepared by this invention do not contain aldehydes, benzene solvents, or heavy metals. The VOC content is extremely low. The natural dyes are non-toxic, renewable, and have unique colors, fully retaining green and environmentally friendly characteristics, which is highly in line with the green development trend of the coating industry. Detailed Implementation

[0035] To more clearly illustrate the technical solution of the present invention, the following embodiments are provided. Unless otherwise stated, the raw materials, reactions, and post-processing methods appearing in the embodiments are all commercially available raw materials and technical methods well known to those skilled in the art.

[0036] The terms "preferred," "more preferably," and "more suitable" used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0037] It should be understood that, except in any operational instance or otherwise indicated, the amounts or all figures representing ingredients used, for example, in the specification and claims, should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise stated, the numerical parameters set forth in the following specification and appended claims are approximate values ​​varying according to the desired performance to be obtained according to the invention.

[0038] The present invention uses the following raw materials: The preparation method of the black dye dispersion includes the following steps: Take 1 kg of fresh maple leaves and tender stem bark, wash and crush them, add 8 L of water, soak at 35℃ for 72 h, and rub three times a day. After removing the residue, introduce air and stir for 1.5 h at a stirring speed of 400 rpm, let stand for 24 h, filter to remove the supernatant, and obtain the black dye dispersion with a solid content of 30%.

[0039] The preparation method of red dye dispersion includes the following steps: take 1 kg of fresh red and blue grass stems and leaves, wash and chop them, add 10 L of water, boil for 15 min, cool and filter to obtain red dye dispersion with a solid content of 30%.

[0040] The preparation method of yellow dye dispersion includes the following steps: take 500 g of dried Buddleja officinalis flowers, crush them, add 5 L of water, boil for 20 min, filter to obtain yellow dye dispersion with a solid content of 25%.

[0041] The preparation method of purple dye dispersion includes the following steps: take 1 kg of fresh purple grass stems and leaves, wash and chop them, add 8 L of water, boil for 20 min, filter to obtain purple dye dispersion with a solid content of 28%.

[0042] The preparation method of blue dye dispersion includes the following steps: take 300 g of butterfly pea flowers, add 4 L of water, boil for 15 minutes, filter to obtain blue dye dispersion with a solid content of 22%.

[0043] Waterborne resin: Waterborne acrylic resin, brand name PU-3757, purchased from Guangdong Qianyou Chemical.

[0044] Dispersant: Name is PEG, brand name is 312, purchased from Guangdong Haoquan Chemical.

[0045] Defoamer: Brand name: defoamer, grade: 532, purchased from Guangdong Haoquan Chemical.

[0046] Thickener: Hydroxyethyl cellulose, brand name 2000, purchased from Shandong Heda Chemical.

[0047] Initiator: Benzoyl peroxide.

[0048] The preparation method of aminated silica includes the following steps: L1. Add 1 g of silicon dioxide to 100 mL of concentrated sulfuric acid-hydrogen peroxide mixed solution (the mass ratio of concentrated sulfuric acid to hydrogen peroxide is 7:3, and the concentration of hydrogen peroxide is 30%), react at 80℃ for 1 h, filter, wash and dry to obtain hydroxylated silicon dioxide. L2. 1 g of the hydroxylated silica was dispersed in 100 mL of toluene. Under a nitrogen atmosphere, 1 mL of 3-aminopropyltriethoxysilane was added, and the mixture was reacted at 80 °C for 5 h. After filtration, washing, and drying, aminated silica was obtained.

[0049] Silica: Grade M757694, purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0050] All water used in this invention is deionized water.

[0051] In this invention, "parts" refers to parts by mass.

[0052] Example 1 A water-based coating based on natural plant dyes, the water-based coating based on natural plant dyes comprising the following components in parts by weight: 15 parts of black dye dispersion 50 parts of water-based acrylic resin 4 parts of modified silica 2 parts dispersant 0.5 parts defoamer Thickener 3 parts 30 parts water.

[0053] The method for preparing water-based coatings based on natural plant dyes includes the following steps: S1. Aminated silica was dispersed in deionized water, tannic acid was added, and the mixture was stirred until homogeneous. Then, glutaraldehyde aqueous solution was added, and the mixture was stirred at room temperature for 24 h. After filtration, washing, and drying, intermediate product 1 was obtained. in, The mass ratio of aminated silica, deionized water, tannic acid, and glutaraldehyde is 2:50:1:5; The mass fraction of glutaraldehyde aqueous solution is 50%; S2. Using ethyl acetate-butyl acetate mixed solvent (ethyl acetate and butyl acetate volume ratio of 3:2) as solvent, the intermediate product 1, triphenylphosphine and hydroquinone were mixed and stirred to disperse evenly. Then, glycidyl methacrylate was slowly added and reacted at 95°C for 24 h. After filtration, washing and drying, intermediate product 2 was obtained. in, The mass ratio of intermediate product 1, triphenylphosphine, hydroquinone, and glycidyl methacrylate is 1:0.05:0.005:1. S3. Using DMF as solvent, intermediate product 2, pentaerythritol triacrylate and hydroxyethyl acrylate are mixed and stirred evenly. An initiator is added, and the mixture is stirred and reacted under a nitrogen atmosphere at 70°C for 5 h. The mixture is then filtered, washed and dried to obtain modified silica. in, The mass ratio of intermediate product 2, pentaerythritol triacrylate, hydroxyethyl acrylate, and initiator is 1:0.5:1:0.01; S4. According to the above mass proportions, all components are mixed evenly and ground until the particle size is ≤30 μm to obtain a water-based coating based on natural plant dyes.

[0054] Example 2 A water-based coating based on natural plant dyes, the water-based coating based on natural plant dyes comprising the following components in parts by weight: 15 parts of red dye dispersion 45 parts of water-based acrylic resin 3 parts modified silica 3 parts dispersant 1 part defoamer 2 parts thickener 35 parts water.

[0055] The preparation method of the water-based coating based on natural plant dyes is the same as in Example 1.

[0056] Example 3 A water-based coating based on natural plant dyes, the water-based coating based on natural plant dyes comprising the following components in parts by weight: 12 parts of yellow dye dispersion 55 parts of water-based acrylic resin 5 parts of modified silica 4 parts dispersant 0.8 parts defoamer 4 parts thickener 25 parts water.

[0057] The preparation method of the water-based coating based on natural plant dyes is the same as in Example 1.

[0058] Example 4 A water-based coating based on natural plant dyes, the water-based coating based on natural plant dyes comprising the following components in parts by weight: 14 parts of purple dye dispersion 50 parts of water-based acrylic resin 4 parts of modified silica 3 parts dispersant 0.8 parts defoamer Thickener 3 parts 30 parts water.

[0059] The preparation method of the water-based coating based on natural plant dyes is the same as in Example 1.

[0060] Example 5 A water-based coating based on natural plant dyes, the water-based coating based on natural plant dyes comprising the following components in parts by weight: 13 parts of blue dye dispersion 48 parts of water-based acrylic resin 4 parts of modified silica 3 parts dispersant 0.8 parts defoamer Thickener 3 parts 32 parts water.

[0061] The preparation method of the water-based coating based on natural plant dyes is the same as in Example 1.

[0062] Example 6 A water-based coating based on natural plant dyes, the water-based coating based on natural plant dyes comprising the following components in parts by weight: 15 parts of mixed dye dispersion 50 parts of water-based acrylic resin 4 parts of modified silica 2 parts dispersant 0.5 parts defoamer Thickener 3 parts 30 parts water; in, The mixed dye dispersion is obtained by mixing black dye dispersion, red dye dispersion, yellow dye dispersion, purple dye dispersion and blue dye dispersion in a mass ratio of 1:1:1:1:1.

[0063] The preparation method of the water-based coating based on natural plant dyes is the same as in Example 1.

[0064] Comparative Example 1 A water-based coating based on natural plant dyes. The difference between this comparative example and Example 1 is that step S1 is omitted. In step S2, the intermediate product 1 is replaced by an equal mass of hydroxylated silica (prepared in step L1 of the preparation method of aminated silica). Other steps and dosages are the same as in Example 1.

[0065] Comparative Example 2 A water-based coating based on natural plant dyes. The difference between this comparative example and Example 1 is that in step S2, the hydroxyethyl acrylate is replaced with ethyl acrylate by mass, while the other steps and dosages are the same as in Example 1.

[0066] Application Examples 1-6 A wine bottle coating, the preparation method of which includes the following steps: The water-based coatings based on natural plant dyes prepared in Examples 1-6 were diluted to the spraying viscosity and sprayed onto the clean glass bottle surface to form a uniform paint film. The coatings were then dried at 100°C for 20 min to obtain a bottle coating with a film thickness of 40 μm. The spraying parameters are: spraying ambient temperature 25±2℃, humidity 50±5%RH, spraying pressure 0.3-0.5 MPa, and spraying distance 20-30 cm.

[0067] Comparative Application Examples 1-2 A wine bottle coating, the preparation method of which includes the following steps: The water-based coatings based on natural plant dyes prepared in Comparative Examples 1-2 were diluted to the spraying viscosity and sprayed onto the clean glass bottle surface to form a uniform paint film. Then, they were dried at 100°C for 20 min to obtain a bottle coating with a film thickness of 40 μm. The spraying parameters are: spraying ambient temperature 25±2℃, humidity 50±5%RH, spraying pressure 0.3-0.5 MPa, and spraying distance 20-30 cm.

[0068] Application Example 7-12 A metallic primer, the preparation method of which includes the following steps: The water-based coatings based on natural plant dyes prepared in Examples 1-6 were diluted to the spraying viscosity and sprayed onto the surface of metal plates that had been degreased and derusted to form a uniform paint film. The coatings were then dried at 100°C for 25 min to obtain a metal primer with a film thickness of 50 μm.

[0069] Compare and contrast with example 3-4 A metallic primer, the preparation method of which includes the following steps: The water-based coatings based on natural plant dyes prepared in Comparative Examples 1 and 2 were diluted to the spraying viscosity and sprayed onto the surface of metal plates that had undergone degreasing and rust removal treatment to form a uniform paint film. The coatings were then dried at 100°C for 25 min to obtain a metal primer with a film thickness of 50 μm.

[0070] Application Example 13-18 A type of floor coating, the preparation method of which includes the following steps: The water-based coatings based on natural plant dyes prepared in Examples 1-6 were diluted to the scraping viscosity and scraped onto the treated concrete floor surface to form a uniform paint film. After drying at 100°C for 30 min, floor paint with a film thickness of 80 μm was obtained.

[0071] Compare and contrast examples 5-6 A type of floor coating, the preparation method of which includes the following steps: The water-based coatings based on natural plant dyes prepared in Comparative Examples 1 and 2 were diluted to the scraping viscosity and scraped onto the treated concrete floor surface to form a uniform paint film. After drying at 100°C for 30 min, floor paint with a film thickness of 80 μm was obtained.

[0072] Test Example 1 The VOC content and chemical composition of the water-based coating based on natural plant dyes prepared in Example 1 were tested.

[0073] Test method: Refer to Appendix B of GB / T 23986-2009, GB / T 30647-2014, GB 30981-2020, GB / T 23990-2009, and GB / T 23993-2009.

[0074] The test results are shown in Table 1.

[0075] Table 1. Test results of VOC content and chemical composition The results above show that the VOC content of the water-based coating based on natural plant dyes of this invention is only 53 g / L, which is better than the limit requirement of ≤80 g / L for water-based coatings in GB 24409-2020, and reduces emissions by more than 85% compared with traditional solvent-based coatings. At the same time, the coating does not contain benzene solvents, formaldehyde, heavy metals, or other harmful substances, exhibiting excellent green and environmentally friendly characteristics.

[0076] Test Example 2 The performance of the bottle coating obtained from Application Example 1-2 was tested in accordance with Case 1-6.

[0077] Test method: Paint film hardness (pencil hardness): Refer to GB / T 6739-2022.

[0078] Adhesion (cross-cut test): Refer to GB / T 9286-1998.

[0079] Salt water resistance (3.5wt% NaCl, 48 h): Refer to GB / T 23999-2018.

[0080] Water resistance (240 h): Refer to GB / T 1733-1993.

[0081] Alcohol resistance (immersion in 50 wt% ethanol for 48 h): Refer to GB / T 23989-2009.

[0082] The test results are shown in Table 2.

[0083] Table 2 Performance test results of wine bottle coating The results above show that the water-based coatings based on natural plant dyes prepared in this invention exhibit excellent performance in key performance indicators such as adhesion, hardness, water resistance, salt water resistance, and alcohol resistance. Adhesion reaches grade 0, hardness exceeds 2H, and water and solvent resistance are good, demonstrating the practical value of water-based coatings based on natural plant dyes. In contrast, the modified silica used in Application Example 1 was not modified with tannic acid and lacked an adsorption active layer, resulting in poorer lightfastness. The modified silica used in Application Example 2 used ethyl acrylate as the polymer monomer, and the cross-linked polymer layer lacked hydroxyl groups, thus resulting in poorer adsorption performance.

[0084] Test Example 3 The performance of the metallic primer obtained from the corresponding use case 7-9 and comparison application example 3-4 was tested.

[0085] Test method: Adhesion (cross-cut test): Refer to GB / T 9286-1998.

[0086] Impact resistance: Refer to GB / T 1732-1993.

[0087] Flexibility: Refer to GB / T 1731-1993.

[0088] Salt spray resistance time: Refer to GB / T 1771-2007.

[0089] The test results are shown in Table 3.

[0090] Table 3 Performance test results of metallic primers The results above show that the water-based coating based on natural plant dyes prepared in this invention, when used as a metal primer, meets the requirements of practical applications in terms of adhesion, impact resistance, flexibility, and salt spray resistance.

[0091] Test Example 4 For example 13, the performance of the floor coating obtained from comparison with example 5-6 is tested.

[0092] Test method: Adhesion (cross-cut test): Refer to GB / T 9286-1998.

[0093] Hardness (pencil hardness): Refer to GB / T 6739-2022.

[0094] Abrasion resistance: Refer to GB / T 1768-2006.

[0095] Chemical resistance: Refer to GB / T 9274-1988.

[0096] The test results are shown in Table 4.

[0097] Table 4 Performance test results of floor coatings The results above show that the water-based coating based on natural plant dyes prepared in this invention exhibits excellent adhesion, hardness, abrasion resistance, and chemical resistance when used as a floor coating, meeting the practical application requirements of floor coatings.

[0098] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0099] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A water-based coating based on natural plant dyes, characterized in that, The water-based coating based on natural plant dyes comprises the following components in parts by weight: 10-20 parts of natural dye dispersion 15-50 parts of water-based resin 2-6 parts of modified silica 0.5-16 parts of auxiliary agent Solvent 20-60 parts; in, The modified silica is obtained by grafting silica with tannic acid to introduce double bonds, followed by copolymerization with pentaerythritol triacrylate and hydroxyacrylate.

2. The water-based coating based on natural plant dyes according to claim 1, characterized in that, The natural dye dispersion is obtained by extraction and purification from natural plants; The natural plants are selected from one or more of the following: maple leaves, red and blue grass, sappanwood, buddleja officinalis, gardenia, turmeric, purple and blue grass, purple and red blue grass, butterfly pea flower, storax, polygonum tinctorium, and woad.

3. The water-based coating based on natural plant dyes according to claim 1, characterized in that, The waterborne resin is selected from one or more of waterborne acrylic resin, waterborne alkyd resin, waterborne epoxy resin, or waterborne polyurethane resin.

4. The water-based coating based on natural plant dyes according to claim 1, characterized in that, The additives are selected from one or more of the following: dispersants, defoamers, thickeners, preservatives, and antioxidants.

5. The method for preparing water-based coatings based on natural plant dyes according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Aminated silica, tannic acid and glutaraldehyde are mixed and stirred to react, yielding intermediate product 1. S2. The intermediate product 1 is blended with glycidyl methacrylate, and the mixture is heated to react under the action of a catalyst and a polymerization inhibitor to obtain intermediate product 2. S3. The intermediate product 2, pentaerythritol triacrylate and hydroxy acrylate are blended together, an initiator is added, and the mixture is reacted under an inert atmosphere and heating conditions to obtain modified silica. S4. Mix all components thoroughly to obtain a water-based coating based on natural plant dyes.

6. The method for preparing water-based coatings based on natural plant dyes according to claim 5, characterized in that, In step S1, the mass ratio of the aminated silica, tannic acid and glutaraldehyde is 1:(0.1-0.9):(1-5).

7. The method for preparing water-based coatings based on natural plant dyes according to claim 5, characterized in that, In step S2, the mass ratio of intermediate product 1 to glycidyl methacrylate is 1:(0.5-1.5).

8. The method for preparing water-based coatings based on natural plant dyes according to claim 5, characterized in that, In step S3, the mass ratio of intermediate product 2, pentaerythritol triacrylate and hydroxyacrylate is 1:(0.1-0.9):(0.5-2).

9. The method for preparing water-based coatings based on natural plant dyes according to claim 5, characterized in that, In step S3, the heating temperature is 60-80℃.

10. The use of the water-based coating based on natural plant dyes as described in any one of claims 1-4 in the surface coating of glass products, wood, metal or flooring.

Images