An environment-friendly coating and a preparation method thereof

Abstract

The application belongs to the technical field of paint, and discloses an environment-friendly paint and a preparation method thereof. The paint is prepared by using castor oil modified thermoplastic acrylic resin and acetylated modified cellulose acetate resin as a film forming main body, matching with an environment-friendly mixed solvent, a leveling agent, a color powder and a dispersing agent, and is prepared by compounding. The compatibility between the resins is optimized by modifying the film forming resin, and the environmental safety and the film forming performance of the paint are simultaneously improved. The preparation method matched with the application adopts a process of step-by-step dissolution, hierarchical dispersion and segmented solvent feeding, improves the dispersion stability and the construction adaptability of the paint, the obtained paint has excellent film forming effect, meets the use requirements of toy coating, and has good industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to an environmentally friendly coating and its preparation method. Background Technology

[0002] Oil-based coatings are widely used in the toy coating industry due to their excellent film-forming properties and high gloss. Currently, in order to adapt to the application scenarios of toys, the industry has put forward higher requirements for the environmental protection, film-forming compatibility and construction adaptability of this type of coating.

[0003] In existing oil-based coatings for toys, the solubility parameters of ordinary thermoplastic acrylic resin and cellulose acetate resin differ. Direct mixing of the two can easily lead to poor compatibility, resulting in appearance defects such as phase separation and pinholes in the coating film, affecting the coating effect. At the same time, the parameters and proportions of conventional resin modification processes are relatively crude, making it difficult to directionally control resin performance and failing to fundamentally improve the compatibility between resins, thus restricting the improvement of the overall performance of the coating.

[0004] In terms of coating preparation and raw material application, existing processes mostly adopt a one-time feeding, mixing and dispersion method without differentiated design based on the characteristics of the resin and solvent. This not only easily leads to insufficient resin dissolution but also results in low pigment dispersion efficiency and easy agglomeration, affecting the storage stability of the coating. Furthermore, the solvent system of some oil-based coatings for toys is insufficient in balancing environmental protection, dissolving power, and workability, making it difficult to simultaneously meet the requirements of low toxicity and environmental protection as well as the coating construction needs of irregularly shaped and small parts of toys, resulting in construction defects such as dry spraying and sagging. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide an environmentally friendly coating and its preparation method, which solves the problems of poor compatibility of toy coating resin systems, and the inability to simultaneously achieve environmental protection, coating performance and construction adaptability.

[0006] To address the above problems, the present invention provides the following technical solution: An environmentally friendly coating, by weight, comprises 20-30 parts castor oil-modified thermoplastic acrylic resin, 3-8 parts acetylated modified cellulose acetate resin, 30-50 parts environmentally friendly mixed solvent, 0.2-1 parts leveling agent, 3-30 parts colorant, and 1-3 parts dispersant; wherein the castor oil-modified thermoplastic acrylic resin is obtained by first esterifying castor oil with maleic anhydride to generate castor oil-based macromolecular monomers, and then copolymerizing them with acrylate monomers using free radicals; wherein the acetylated modified cellulose acetate resin is obtained by acetylation of cellulose pulp with acetic anhydride under the action of a catalyst after activation with glacial acetic acid; wherein the colorant is one or a mixture of two of inorganic and organic colorants, wherein the inorganic colorant is one or more of titanium dioxide, zinc oxide, iron oxide, and ultramarine, and the organic colorant is one or more of azo colorants and phthalocyanine colorants.

[0007] Further, the method for preparing the castor oil-modified thermoplastic acrylic resin involves mixing castor oil and maleic anhydride at a mass ratio of 10:1-15:1, adding 0.1-0.3% p-toluenesulfonic acid (by mass of castor oil) as a catalyst, and reacting at 80-90℃ for 2-4 hours to obtain castor oil-based macromonomers. The castor oil-based macromonomers, butyl acrylate, methyl methacrylate, and hydroxyethyl methacrylate are then mixed at a mass ratio of 1:2:3:1, and 0.5-1.0% benzoyl peroxide (by mass of total monomers) is added as an initiator. The mixture is heated to 75-85℃ under nitrogen protection and reacted for 4-6 hours. The mixture is then cooled to below 40℃ and discharged to obtain the castor oil-modified thermoplastic acrylic resin. Through a two-step method of esterification graft polymerization of double bonds followed by free radical copolymerization, the flexible long chains of castor oil are directionally grafted onto the main chain of the acrylic resin, simultaneously improving the resin's flexibility, adhesion, and bio-based environmental friendliness at the molecular structure level.

[0008] Further, the method for preparing the acetylated modified cellulose acetate resin is as follows: cellulose pulp is mixed with glacial acetic acid at a mass ratio of 1:5-1:10, and soaked at 25-35℃ for 1-2 hours to obtain activated cellulose; acetic anhydride and concentrated sulfuric acid (0.5-1.0% by mass of activated cellulose) are added to the activated cellulose as catalysts, with an acetic anhydride to activated cellulose mass ratio of 3:1-5:1, and reacted at 40-50℃ for 2-3 hours; sodium carbonate solution is added to neutralize the system to a pH of 6-7; the mixture is washed with water until the conductivity of the filtrate is ≤50μS / cm; and dried at 60-80℃ until the moisture content is ≤3%, yielding an acetylated modified cellulose acetate resin with a degree of acetylation of 52-56%. First, soaking in glacial acetic acid breaks the intramolecular hydrogen bonds of cellulose to enhance the reactivity, and then the degree of acetylation of the resin is controlled by the acetylation reaction to match the solubility of the modified resin with that of castor oil-modified acrylic resin.

[0009] Furthermore, by weight, the environmentally friendly mixed solvent comprises 15-25 parts of tributyl acetyl citrate, 10-15 parts of tributyl citrate, and 5-10 parts of limonene. Utilizing the complementary gradient characteristics of the three components in terms of solubility, polarity, and evaporation rate, the process ensures that the two modified resins gradually achieve molecular-level miscibility during the staged solvent addition process to form a homogeneous composite resin liquid. This achieves the environmental requirements of being free of benzene, ketones, ethylene glycol ethers, and phthalic acid plasticizers, while simultaneously controlling the solvent evaporation rate during coating application to avoid problems such as dry spraying and sagging in toy coating, thus adapting to the application needs of toy coating.

[0010] Furthermore, the leveling agent is a polyacrylate leveling agent or a silicone-modified acrylate leveling agent. Selecting a polyacrylate or silicone-modified acrylate leveling agent with excellent compatibility with the composite resin system of this invention reduces the surface tension of the coating system, improves the spreadability of the coating film, and effectively eliminates coating defects such as pinholes and fisheyes.

[0011] Furthermore, the dispersant is a block copolymer dispersant or a fatty acid polyethylene glycol ester dispersant. By selecting a block copolymer or fatty acid polyethylene glycol ester dispersant compatible with the pigment system and composite resin system of this invention, the dispersant's anchoring groups tightly adsorb onto the surface of the pigment particles. Its solvated long-chain segments form stable steric hindrance in the composite resin system, effectively preventing the pigment particles from agglomerating and settling.

[0012] The environmentally friendly coating of this invention, through the directional graft copolymerization modification of castor oil, endows the coating film with good flexibility and impact resistance while retaining the excellent film-forming properties of thermoplastic acrylic resin. It is simultaneously compounded with acetylated modified cellulose acetate resin, and the compatibility between cellulose molecules and acrylic resin is optimized by directional modification of cellulose molecules. This avoids phase separation and coating appearance defects that are prone to occur in conventional compounding schemes from the root of the film-forming system. It is further combined with environmentally friendly mixed solvents, leveling agents and dispersants adapted to the characteristics of the system, and environmentally friendly pigments to construct a complete formula. While meeting the stringent environmental requirements of toy coatings, it achieves synergistic optimization of the coating's comprehensive film-forming performance, storage stability and application compatibility.

[0013] As a general inventive concept, the present invention also provides a method for preparing the environmentally friendly coating as described above, comprising the following steps: S1. The environmentally friendly mixed solvent is divided into a first solvent component, a second solvent component and a third solvent component according to the weight parts. The acetylated modified cellulose acetate resin is added to the first solvent component and stirred at a gradient temperature until completely dissolved to obtain a cellulose resin liquid. Castor oil modified thermoplastic acrylic resin and the second solvent component are added to the cellulose resin liquid and stirred at a constant temperature until the resins are completely miscible to obtain a homogeneous composite resin liquid. S2. Take a portion of the composite resin liquid, mix it with color powder and dispersant, pre-disperse it, and then mill it to obtain a color paste; mix the color paste with the remaining composite resin liquid and disperse it at high speed to obtain a mixture; S3. Add leveling agent and third solvent component to the mixture, stir at low speed until uniform, let stand to degas, and then filter to obtain the finished product.

[0014] Further, in step S1, the first solvent component is the total amount of tributyl citrate and 50-70% of the total mass of tributyl citrate, the second solvent component is the remaining 30-50% of tributyl citrate, and the third solvent component is the total amount of limonene; the gradient temperature-controlled stirring involves first heating to 30-40℃ and stirring at 500-800 rpm for 20-30 minutes, then heating to 45-55℃ and stirring at 300-500 rpm for 30-40 minutes; the stirring speed during constant temperature stirring is 400-600 rpm, and the stirring time is 20-30 minutes. To address the difference in solubility polarity between the two modified resins in this invention, a first solvent component with high solubility is first used in conjunction with gradient temperature-controlled stirring to achieve full swelling and complete dissolution of the acetylated modified cellulose acetate resin. Then, the polarity of the system is adjusted by the second solvent component and combined with constant temperature stirring parameters to achieve molecular-level miscibility between the castor oil-modified thermoplastic acrylic resin and the cellulose resin liquid. This ensures the uniformity and stability of the composite resin liquid from the perspective of process parameters.

[0015] Further, in step S2, the composite resin liquid used accounts for 20-30% of the total mass of the composite resin liquid; the pre-dispersion speed is 800-1200 rpm, and the dispersion time is 15-20 min; the sand milling uses zirconium bead media, and the material fineness is ≤10 μm; the high-speed dispersion speed is 1000-1500 rpm, and the dispersion time is 10-20 min. By constructing a low-viscosity pre-dispersion system with a low proportion of composite resin liquid, the wetting and anchoring efficiency of the dispersant on the pigment particles is improved. Combined with zirconium bead sand milling, the fineness of the pigment is controlled below 10 μm. Then, high-speed dispersion is used to achieve uniform fusion of the pigment paste and the main resin liquid. The spatial steric hindrance effect of the long resin chain further stabilizes the dispersion state of the pigment, effectively avoiding pigment agglomeration and sedimentation, while ensuring the storage stability of the coating.

[0016] Furthermore, in step S3, the low-speed stirring speed is 200-400 rpm, and the stirring time is 10-15 min; the temperature for standing degassing is 20-30℃, and the standing time is 30-60 min; filtration is performed using a 150-200 mesh filter. Low-speed stirring avoids introducing a large number of air bubbles when the leveling agent and slow-drying limonene solvent are added. Combined with standing degassing at room temperature, this thoroughly eliminates tiny air bubbles in the system. Finally, filtration removes undissolved particles and impurities from the system.

[0017] The method for preparing the environmentally friendly coating of this invention, through functionalized segmented design of the environmentally friendly mixed solvent, matches the differentiated dissolution and miscibility requirements of the resin, ensuring the uniformity and stability of the composite film-forming system from the process level; to address the requirements of pigment dispersion and long-term storage stability of the system, a dispersion design using graded utilization of resin base material is adopted to enhance the wetting and anchoring effect and dispersion stability of pigment; at the same time, combining the solvent volatility characteristics and on-site application compatibility requirements, a design of post-application of functional additives and slow-drying components is adopted to regulate the application window and film-forming effect of the coating; finally, through a process design highly compatible with the formulation system, the environmental friendliness, film-forming performance and application compatibility of the coating are synergistically optimized.

[0018] Compared with the prior art, the advantages of the present invention are: (1) This invention solves the compatibility problem of conventional acrylic resin and cellulose acetate resin compounding by directionally modified dual resin film forming system, and achieves synergistic improvement of coating film flexibility, impact resistance and hardness, breaking through the inherent performance bottleneck of single film forming resin that is hard and brittle and soft and sticky, and adapts to the use needs of toy products. (2) The present invention uses an environmentally friendly mixed solvent, combined with a film-forming resin modified with bio-based castor oil. The raw materials meet the environmental and safety requirements of coatings for toys. At the same time, through the gradient design of solvent components, the dissolution capacity of the modified resin and the stability of the system are taken into account, solving the industry pain point that environmental protection and dissolution performance cannot be taken into account at the same time. (3) The present invention strengthens the wetting and anchoring effect of the dispersant on the pigment particles by designing a graded dispersion process that is highly compatible with the formulation system. Combined with the stable steric hindrance effect formed by the composite resin system, it effectively inhibits the agglomeration and sedimentation of pigment particles and greatly improves the long-term storage stability of the coating. (4) This invention regulates the solvent evaporation rhythm during the coating process by using solvent functionalization and post-drying component design, which broadens the construction window and solves coating defects such as dry spraying, sagging, and pinholes that are prone to occur during the coating of toy irregular parts and small parts. (5) The preparation process of the dual-modified resin and the overall production process of the coating can be realized using conventional equipment in the industry. The process parameters are reasonable and controllable. Those skilled in the art can prepare it stably and repeatedly. There are no extreme process conditions or special equipment requirements. It has good industrial production and promotion value. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation method of the environmentally friendly coating in Embodiment 1 of the present invention. Detailed Implementation

[0020] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0021] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods. Example

[0023] An environmentally friendly coating of the present invention comprises, by weight, 30 parts of castor oil modified thermoplastic acrylic resin, 8 parts of acetylated modified cellulose acetate resin, 50 parts of environmentally friendly mixed solvent, 1 part of organosilicon modified acrylate leveling agent, 30 parts of phthalocyanine blue powder, and 3 parts of block copolymer dispersant; wherein the environmentally friendly mixed solvent is composed of 25 parts of tributyl acetylacetonate, 15 parts of tributyl citrate, and 10 parts of limonene.

[0024] The method for preparing castor oil-modified thermoplastic acrylic resin is as follows: castor oil and maleic anhydride are mixed at a mass ratio of 15:1, and 0.3% of p-toluenesulfonic acid (by mass of castor oil) is added as a catalyst. The mixture is reacted at 90°C for 2 hours to obtain castor oil-based macromonomers. Castor oil-based macromonomers, butyl acrylate, methyl methacrylate, and hydroxyethyl methacrylate are mixed at a mass ratio of 1:2:3:1, and 1.0% of benzoyl peroxide (by mass of total monomers) is added as an initiator. The mixture is heated to 85°C under nitrogen protection and reacted for 4 hours. The mixture is then cooled to below 40°C and discharged to obtain castor oil-modified thermoplastic acrylic resin.

[0025] The method for preparing the acetylated modified cellulose acetate resin is as follows: cellulose pulp and glacial acetic acid are mixed at a mass ratio of 1:10 and soaked at 35°C for 1 hour to obtain activated cellulose; acetic anhydride and concentrated sulfuric acid (1.0% of the mass of activated cellulose) are added to the activated cellulose as catalysts, with an acetic anhydride to activated cellulose mass ratio of 5:1, and the mixture is reacted at 50°C for 2 hours; sodium carbonate solution is added to neutralize the system to pH 7; the mixture is washed with water until the conductivity of the filtrate is ≤50 μS / cm; and the mixture is dried at 80°C until the moisture content is ≤3% to obtain an acetylated modified cellulose acetate resin with a degree of acetylation of 56%.

[0026] refer to Figure 1 The method for preparing the environmentally friendly coating in this embodiment includes the following steps: S1. The environmentally friendly mixed solvent is divided into a first solvent component, a second solvent component, and a third solvent component. The first solvent component consists of the total amount of tributyl citrate and 70% of the total mass of tributyl citrate. The second solvent component consists of the remaining 30% of tributyl citrate. The third solvent component consists of the total amount of limonene. Acetylated modified cellulose acetate resin is added to the first solvent component. The mixture is first heated to 40°C and stirred at 800 rpm for 20 minutes. Then, the mixture is heated to 55°C and stirred at 500 rpm for 30 minutes until completely dissolved, resulting in a cellulose resin solution. Castor oil-modified thermoplastic acrylic resin and the second solvent component are added to the cellulose resin solution. The mixture is stirred at 600 rpm for 20 minutes until the resins are completely miscible, resulting in a homogeneous composite resin solution. S2. Take 30% of the total mass of the composite resin liquid and mix it with phthalocyanine blue powder and block copolymer dispersant. Pre-disperse at 1200 rpm for 15 min. Grind the mixture with zirconium beads as the medium until the fineness of the material is ≤10 μm to obtain a color paste. Mix the color paste with the remaining composite resin liquid and disperse at 1500 rpm for 10 min to obtain a mixture. S3. Add the silicone-modified acrylate leveling agent and the third solvent component to the mixture, stir at a low speed of 400 rpm for 10 minutes until uniform, let stand at 30°C for 30 minutes to degas, and filter with a 200-mesh filter to obtain the finished product. Example

[0027] An environmentally friendly coating of the present invention comprises, by weight, 25 parts castor oil modified thermoplastic acrylic resin, 5 parts acetylated modified cellulose acetate resin, 40 parts environmentally friendly mixed solvent, 0.6 parts polyacrylate leveling agent, 15 parts iron oxide red powder, and 2 parts fatty acid polyethylene glycol ester dispersant; wherein the environmentally friendly mixed solvent is composed of 20 parts tributyl acetylacetonate, 12 parts tributyl citrate, and 8 parts limonene.

[0028] The method for preparing castor oil-modified thermoplastic acrylic resin is as follows: castor oil and maleic anhydride are mixed at a mass ratio of 12:1, and 0.2% of p-toluenesulfonic acid by mass of castor oil is added as a catalyst. The mixture is reacted at 85°C for 3 hours to obtain castor oil-based macromonomers. Castor oil-based macromonomers, butyl acrylate, methyl methacrylate, and hydroxyethyl methacrylate are mixed at a mass ratio of 1:2:3:1, and 0.8% of benzoyl peroxide by mass of total monomers is added as an initiator. The mixture is heated to 80°C under nitrogen protection and reacted for 5 hours. The mixture is then cooled to below 40°C and discharged to obtain castor oil-modified thermoplastic acrylic resin.

[0029] The method for preparing the acetylated modified cellulose acetate resin is as follows: cellulose pulp and glacial acetic acid are mixed at a mass ratio of 1:8 and soaked at 30°C for 1.5 h to obtain activated cellulose; acetic anhydride and concentrated sulfuric acid (0.8% by mass of activated cellulose) are added to the activated cellulose as catalysts, with an acetic anhydride to activated cellulose mass ratio of 4:1, and the reaction is carried out at 45°C for 2.5 h; sodium carbonate solution is added to neutralize the system to a pH of 6.5; the mixture is washed with water until the conductivity of the filtrate is ≤50 μS / cm; and the mixture is dried at 70°C until the moisture content is ≤3% to obtain an acetylated modified cellulose acetate resin with a degree of acetylation of 54%.

[0030] The method for preparing the environmentally friendly coating in this embodiment includes the following steps: S1. The environmentally friendly mixed solvent is divided into a first solvent component, a second solvent component, and a third solvent component. The first solvent component consists of the total amount of tributyl citrate and 60% of the total mass of tributyl citrate. The second solvent component consists of the remaining 40% of tributyl citrate. The third solvent component consists of the total amount of limonene. Acetylated modified cellulose acetate resin is added to the first solvent component. The mixture is first heated to 35°C and stirred at 650 rpm for 25 minutes. Then, the mixture is heated to 50°C and stirred at 400 rpm for 35 minutes until completely dissolved, resulting in a cellulose resin solution. Castor oil-modified thermoplastic acrylic resin and the second solvent component are added to the cellulose resin solution. The mixture is stirred at 500 rpm for 25 minutes until the resins are completely miscible, resulting in a homogeneous composite resin solution. S2. Take 25% of the total mass of the composite resin liquid and mix it with iron oxide red powder and fatty acid polyethylene glycol ester dispersant. Pre-disperse at 1000 rpm for 18 min, and mill with zirconium beads as the medium until the fineness of the material is ≤10 μm to obtain a color paste. Mix the color paste with the remaining composite resin liquid and disperse at 1200 rpm for 15 min to obtain a mixture. S3. Add polyacrylate leveling agent and third solvent component to the mixture, stir at low speed of 300 rpm for 12 min until uniform, let stand at 25℃ for 45 min to degas, and filter with 180 mesh to obtain the finished product. Example

[0031] An environmentally friendly coating of the present invention comprises, by weight, 20 parts castor oil modified thermoplastic acrylic resin, 3 parts acetylated modified cellulose acetate resin, 30 parts environmentally friendly mixed solvent, 0.2 parts polyacrylate leveling agent, 3 parts titanium dioxide powder, and 1 part block copolymer dispersant; wherein the environmentally friendly mixed solvent is composed of 15 parts tributyl acetylacetonate, 10 parts tributyl citrate, and 5 parts limonene.

[0032] The method for preparing castor oil-modified thermoplastic acrylic resin is as follows: castor oil and maleic anhydride are mixed at a mass ratio of 10:1, and 0.1% of p-toluenesulfonic acid by mass of castor oil is added as a catalyst. The mixture is reacted at 80°C for 4 hours to obtain castor oil-based macromonomers. Castor oil-based macromonomers, butyl acrylate, methyl methacrylate, and hydroxyethyl methacrylate are mixed at a mass ratio of 1:2:3:1, and 0.5% of benzoyl peroxide by mass of total monomers is added as an initiator. The mixture is heated to 75°C under nitrogen protection and reacted for 6 hours. The mixture is then cooled to below 40°C and discharged to obtain castor oil-modified thermoplastic acrylic resin.

[0033] The method for preparing the acetylated modified cellulose acetate resin is as follows: cellulose pulp and glacial acetic acid are mixed at a mass ratio of 1:5 and soaked at 25°C for 2 hours to obtain activated cellulose; acetic anhydride and concentrated sulfuric acid (0.5% by mass of activated cellulose) are added to the activated cellulose as catalysts, with an acetic anhydride to activated cellulose mass ratio of 3:1, and the mixture is reacted at 40°C for 3 hours; sodium carbonate solution is added to neutralize the system to pH 6; the mixture is washed with water until the conductivity of the filtrate is ≤50μS / cm; and the mixture is dried at 60°C until the moisture content is ≤3% to obtain an acetylated modified cellulose acetate resin with a degree of acetylation of 52%.

[0034] The method for preparing the environmentally friendly coating in this embodiment includes the following steps: S1. The environmentally friendly mixed solvent is divided into a first solvent component, a second solvent component, and a third solvent component. The first solvent component consists of the total amount of tributyl citrate and 50% of the total mass of tributyl citrate. The second solvent component consists of the remaining 50% of tributyl citrate. The third solvent component consists of the total amount of limonene. Acetylated modified cellulose acetate resin is added to the first solvent component. The mixture is first heated to 30°C and stirred at 500 rpm for 30 minutes. Then, the mixture is heated to 45°C and stirred at 300 rpm for 40 minutes until completely dissolved, resulting in a cellulose resin solution. Castor oil-modified thermoplastic acrylic resin and the second solvent component are added to the cellulose resin solution. The mixture is stirred at 400 rpm for 30 minutes until the resins are completely miscible, resulting in a homogeneous composite resin solution. S2. Take 20% of the total mass of the composite resin liquid and mix it with titanium dioxide powder and block copolymer dispersant. Pre-disperse at 800 rpm for 20 min. Grind the material with zirconium beads as the medium until the fineness is ≤10 μm to obtain a color paste. Mix the color paste with the remaining composite resin liquid and disperse at 1000 rpm for 20 min to obtain a mixture. S3. Add polyacrylate leveling agent and third solvent component to the mixture, stir at low speed of 200 rpm for 15 min until uniform, let stand at 20℃ for 60 min to degas, and filter with a 150 mesh filter to obtain the finished product.

[0035] Comparative Example 1 The preparation method of the environmentally friendly coating in this comparative example includes the following steps: S1. Mix 20 parts of n-propyl acetate, 12 parts of propylene glycol methyl ether acetate and 8 parts of limonene to obtain an environmentally friendly mixed solvent. Add 25 parts of commercially available thermoplastic acrylic resin and 5 parts of commercially available unmodified cellulose acetate resin to the environmentally friendly mixed solvent. Stir at 500 rpm for 30 minutes at 45°C until the resin is completely dissolved to obtain a resin liquid. S2. Add 15 parts of iron oxide red powder and 2 parts of fatty acid polyethylene glycol ester dispersant to the resin liquid, disperse at a high speed of 1200 rpm for 30 min, and grind with zirconium beads as the medium until the fineness of the material is ≤10μm to obtain the mixture. S3. Add 0.6 parts of polyacrylate leveling agent to the mixture, stir at a low speed of 300 rpm for 12 minutes until uniform, let stand at 25°C to degas for 45 minutes, and filter with a 180-mesh filter to obtain the finished product.

[0036] Comparative Example 2 The preparation method of the environmentally friendly coating in this comparative example includes the following steps: S1. The environmentally friendly mixed solvent is divided into a first solvent component, a second solvent component, and a third solvent component. The environmentally friendly mixed solvent consists of 20 parts of tributyl citrate, 12 parts of tributyl citrate, and 8 parts of limonene. The first solvent component is the total amount of tributyl citrate and 60% of the total mass of tributyl citrate. The second solvent component is the remaining 40% of tributyl citrate. The third solvent component is the total amount of limonene. 30 parts of castor oil-modified thermoplastic acrylic resin are added to the first solvent component, and the mixture is first heated to 35°C. The mixture was stirred at 650 rpm for 25 minutes, then heated to 50°C and stirred at 400 rpm for 35 minutes until completely dissolved to obtain a resin solution. A second solvent component was added to the resin solution and stirred at 500 rpm for 25 minutes until the system was homogeneous to obtain a composite resin solution. The castor oil modified thermoplastic acrylic resin was obtained by esterifying castor oil and maleic anhydride at a mass ratio of 12:1, and then copolymerizing it with butyl acrylate, methyl methacrylate, and hydroxyethyl methacrylate at a mass ratio of 1:2:3:1. S2. Take 25% of the total mass of the composite resin liquid and mix it with 15 parts of iron oxide red powder and 2 parts of fatty acid polyethylene glycol ester dispersant. Pre-disperse at 1000 rpm for 18 min, and then grind the material with zirconium beads as the medium until the fineness of the material is ≤10 μm to obtain a color paste. Mix the color paste with the remaining composite resin liquid and disperse at 1200 rpm for 15 min to obtain a mixture. S3. Add 0.6 parts of polyacrylate leveling agent and the third solvent component to the mixture, stir at a low speed of 300 rpm for 12 minutes until uniform, let stand at 25°C to degas for 45 minutes, and filter with a 180 mesh filter to obtain the finished product.

[0037] Comparative Example 3 The preparation method of the environmentally friendly coating in this comparative example includes the following steps: S1. Mix 20 parts of tributyl acetylacetic acid, 12 parts of propylene glycol methyl ether acetate, and 8 parts of limonene to obtain an environmentally friendly mixed solvent. Add 5 parts of acetylated modified cellulose acetate resin and 25 parts of castor oil modified thermoplastic acrylic resin to the environmentally friendly mixed solvent. Stir at 500 rpm for 40 minutes at 50°C until the resins are completely miscible to obtain a composite resin liquid. The acetylated modified cellulose acetate resin is obtained by acetylation of cellulose pulp with acetic anhydride after activation with glacial acetic acid, with a degree of acetylation of 54%. The castor oil modified thermoplastic acrylic resin is obtained by copolymerizing castor oil with maleic anhydride and then with acrylate monomers. S2. Add 15 parts of iron oxide red powder and 2 parts of fatty acid polyethylene glycol ester dispersant to the composite resin liquid, disperse at a high speed of 1200 rpm for 30 min, and grind with zirconium beads as the medium until the fineness of the material is ≤10μm to obtain the mixture. S3. Add 0.6 parts of polyacrylate leveling agent and 8 parts of limonene to the mixture, stir at a low speed of 300 rpm for 12 minutes until uniform, let stand at 25°C for 45 minutes to degas, and filter with a 180-mesh filter to obtain the finished product.

[0038] Comparative Example 4 The preparation method of the environmentally friendly coating in this comparative example includes the following steps: S1. The environmentally friendly mixed solvent is divided into a first solvent component, a second solvent component, and a third solvent component. The environmentally friendly mixed solvent consists of 20 parts of tributyl citrate, 12 parts of tributyl citrate, and 8 parts of limonene. The first solvent component is the total amount of tributyl citrate and 60% of the total mass of tributyl citrate. The second solvent component is the remaining 40% of tributyl citrate. The third solvent component is the total amount of limonene. Five parts of acetylated modified cellulose acetate resin are added to the first solvent component. The mixture is first heated to 35°C and stirred at 650 rpm for 25 minutes. The mixture is then heated to 50°C and stirred at a constant temperature of 400 rpm for 35 minutes until completely dissolved to obtain a cellulose resin solution. The acetylated modified cellulose acetate resin is obtained by acetylation of cellulose pulp with acetic anhydride after activation with glacial acetic acid, with a degree of acetylation of 54%. 25 parts of a blend of castor oil and thermoplastic acrylic resin and a second solvent component are added to the cellulose resin solution and stirred at a constant temperature of 500 rpm for 25 minutes until completely miscible to obtain a homogeneous composite resin solution. The blend is prepared by mixing castor oil and ordinary thermoplastic acrylic resin at a mass ratio of 12:88. S2. Take 25% of the total mass of the composite resin liquid and mix it with 15 parts of iron oxide red powder and 2 parts of fatty acid polyethylene glycol ester dispersant. Pre-disperse at 1000 rpm for 18 min, and then grind the material with zirconium beads as the medium until the fineness of the material is ≤10 μm to obtain a color paste. Mix the color paste with the remaining composite resin liquid and disperse at 1200 rpm for 15 min to obtain a mixture. S3. Add 0.6 parts of polyacrylate leveling agent and the third solvent component to the mixture, stir at a low speed of 300 rpm for 12 minutes until uniform, let stand at 25°C to degas for 45 minutes, and filter with a 180 mesh filter to obtain the finished product.

[0039] The testing method is as follows: VOC content: VOC content was tested using headspace gas chromatography under the chromatographic conditions specified in GB18581-2020, in conjunction with the GB6675 toy safety standard. Coating appearance: A coating with a dry film thickness of 20-30 μm was prepared according to the process of this invention. After curing at 25°C and 60% relative humidity for 72 hours, the surface of the coating was visually observed under natural light to check for defects such as pinholes, phase separation, and particles. The compatibility between resins was evaluated accordingly. Pencil Hardness: The pencil hardness test was conducted using Zhonghua brand pencils in accordance with ISO15184 standard, and the highest pencil hardness with no scratches on the coating surface was taken as the final test result. Flexibility: According to GB / T1731 standard, the coating was subjected to repeated 180° bending tests using a 2mm shaft at room temperature, and the maximum number of bends without cracking or peeling was recorded. Impact resistance: A 500g steel flat-bottomed weight is dropped freely from a height of 30cm onto three non-overlapping test points on the coating surface. The coating is then visually inspected to see if there are any signs of paint peeling, scratches, or damage. Storage stability: The coating sample was sealed and placed in a constant temperature environment of 25℃ and stored statically. Visual observation was carried out every 7 days. The judgment criteria were that there was no visible layering or pigment agglomeration and the height of the settling layer was ≤1% of the total height of the sample. The longest storage days that the sample met the criteria were recorded. Application: Using a conventional pneumatic spray gun for toy painting, with spray gun air pressure set to 0.3-0.5MPa and spraying distance to 20-30cm, the paint is sprayed onto the ABS irregularly shaped toy substrate to prepare a dry film thickness of 20-30μm. The application process is visually observed for dry spraying or sagging, and the uniformity of the coating is directly evaluated.

[0040] Table 1: Experimental Results of Examples 1-3 and Comparative Examples 1-4

[0041] In summary, referring to Table 1, all test data for the examples showed excellent performance. Because a dual-modified film-forming system was constructed using castor oil-modified thermoplastic acrylic resin and acetylated cellulose acetate resin, combined with an environmentally friendly mixed solvent, and employing a series of processes including staged solvent feeding, gradient temperature-controlled dissolution, and graded dispersion, molecular-level compatibility of the resin was achieved. Therefore, VOCs were not detected, and the coating surface showed no visual defects. The flexible long chains grafted with castor oil and the environmentally friendly solvent formed a synergistic effect, significantly improving the coating's flexibility and impact resistance. The graded dispersion process enhanced the dispersion stability of the pigments, resulting in excellent storage stability of the coating. Staged solvent feeding controlled the evaporation rate, making it suitable for the spraying requirements of irregularly shaped toy parts, and ensuring defect-free application. Each comparative example had shortcomings to varying degrees. Comparative example 1 did not use modified resin and matching process, resulting in poor resin compatibility and trace VOC detection. Comparative example 2 lacked acetylated modified cellulose acetate resin, resulting in no synergistic effect between the two resins, and the coating film showed slight pinholes and decreased flexibility. Comparative example 3 did not implement segmented solvent feeding and graded dispersion, resulting in insufficient resin dissolution and pigment dispersion, and the coating film contained fine particles and had poor storage stability. Comparative example 4 used castor oil and resin blending, which failed to form a stable flexible molecular structure, resulting in insufficient impact resistance and flexibility of the coating film.

Claims

1. An environmentally friendly coating, characterized in that: By weight, it includes 20-30 parts castor oil modified thermoplastic acrylic resin, 3-8 parts acetylated modified cellulose acetate resin, 30-50 parts environmentally friendly mixed solvent, 0.2-1 parts leveling agent, 3-30 parts color powder, and 1-3 parts dispersant; The method for preparing castor oil-modified thermoplastic acrylic resin is as follows: castor oil and maleic anhydride are mixed at a mass ratio of 10:1-15:1, and 0.1-0.3% of p-toluenesulfonic acid by mass of castor oil is added as a catalyst. The mixture is reacted at 80-90℃ for 2-4 hours to obtain castor oil-based macromonomers. Castor oil-based macromonomers, butyl acrylate, methyl methacrylate, and hydroxyethyl methacrylate are mixed at a mass ratio of 1:2:3:1, and 0.5-1.0% of benzoyl peroxide by mass of total monomers is added as an initiator. The mixture is heated to 75-85℃ under nitrogen protection and reacted for 4-6 hours. The mixture is then cooled to below 40℃ and discharged to obtain castor oil-modified thermoplastic acrylic resin. The method for preparing the acetylated modified cellulose acetate resin is as follows: cellulose pulp and glacial acetic acid are mixed at a mass ratio of 1:5-1:10 and soaked at 25-35℃ for 1-2 hours to obtain activated cellulose; acetic anhydride and concentrated sulfuric acid (0.5-1.0% by mass of activated cellulose) are added to the activated cellulose as catalysts, with the mass ratio of acetic anhydride to activated cellulose being 3:1-5:1; the reaction is carried out at 40-50℃ for 2-3 hours; sodium carbonate solution is added to neutralize the system to a pH of 6-7; the filtrate is washed until the conductivity is ≤50μS / cm; and the filtrate is dried at 60-80℃ until the moisture content is ≤3% to obtain an acetylated modified cellulose acetate resin with a degree of acetylation of 52-56%. The environmentally friendly mixed solvent comprises, by weight, 15-25 parts of tributyl citrate, 10-15 parts of tributyl citrate, and 5-10 parts of limonene; The leveling agent is a polyacrylate leveling agent or a silicone-modified acrylate leveling agent; The dispersant is a block copolymer dispersant or a fatty acid polyethylene glycol ester dispersant; The color powder is one or a mixture of two of inorganic and organic color powders, wherein the inorganic color powder is one or more of titanium dioxide, zinc oxide, iron oxide, and ultramarine, and the organic color powder is one or more of azo color powder and phthalocyanine color powder.

2. A method for preparing the environmentally friendly coating as described in claim 1, characterized in that: Includes the following steps, S1. The environmentally friendly mixed solvent is divided into a first solvent component, a second solvent component and a third solvent component according to the weight parts. The acetylated modified cellulose acetate resin is added to the first solvent component and stirred at a gradient temperature until completely dissolved to obtain a cellulose resin liquid. Castor oil modified thermoplastic acrylic resin and the second solvent component are added to the cellulose resin liquid and stirred at a constant temperature until the resins are completely miscible to obtain a homogeneous composite resin liquid. S2. Take a portion of the composite resin liquid, mix it with color powder and dispersant, pre-disperse it, and then mill it to obtain a color paste; mix the color paste with the remaining composite resin liquid and disperse it at high speed to obtain a mixture; S3. Add leveling agent and third solvent component to the mixture, stir at low speed until uniform, let stand to degas, and then filter to obtain the finished product.

3. The method for preparing the environmentally friendly coating according to claim 2, characterized in that: In step S1, the first solvent component is the total amount of tributyl citrate and 50-70% of the total mass of tributyl citrate; the second solvent component is the remaining 30-50% of tributyl citrate; and the third solvent component is the total amount of limonene. The gradient temperature-controlled stirring involves first heating to 30-40°C and stirring at 500-800 rpm for 20-30 minutes, then heating to 45-55°C and stirring at 300-500 rpm for 30-40 minutes. The stirring speed during constant temperature stirring is 400-600 rpm, and the stirring time is 20-30 minutes.

4. The method for preparing the environmentally friendly coating according to claim 2, characterized in that: In step S2, the composite resin liquid used accounts for 20-30% of the total mass of the composite resin liquid; the pre-dispersion speed is 800-1200 rpm, and the dispersion time is 15-20 min; the sand mill uses zirconium bead media and the material fineness is ≤10μm; the high-speed dispersion speed is 1000-1500 rpm, and the dispersion time is 10-20 min.

5. The method for preparing the environmentally friendly coating according to claim 2, characterized in that: In step S3, the low-speed stirring speed is 200-400 rpm, and the stirring time is 10-15 min; the temperature for standing and degassing is 20-30℃, and the standing time is 30-60 min; filtration is carried out using a 150-200 mesh filter.

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