Coating film for incense beads, and preparation method and application thereof

Abstract

The application provides a coating film for a combined incense bead and a preparation method and application thereof, and belongs to the technical field of polymers. The coating film is divided into an inner coating liquid and an outer coating liquid layer. The inner coating liquid contains temperature-sensitive grafted cyclodextrin, cellulose acetate, a plasticizer and hydrophobic nano inorganic molecules. The outer coating liquid contains water-based polyurethane, a hardener, fluorocarbon surface additives and a crosslinking agent. The application realizes the synergistic optimization of performance through the composite structure of the intelligent controlled-release inner layer and the strong protective outer layer. The inner layer realizes the stable release of fragrance at room temperature and the intelligent slow release triggered by body temperature. The outer layer constructs a durable barrier with high hardness, wear resistance, ultraviolet resistance and hydrophobicity. The design integrates intelligent fragrance saving and long-lasting protection, effectively overcomes the defect of single function of traditional coating materials, and significantly improves the user experience and service life of solid incense products.

Description

Technical Field

[0001] This invention belongs to the field of polymer technology, and particularly relates to a coating film for blended fragrance beads, its preparation method and application. Background Technology

[0002] Solid fragrance products, such as blended fragrance beads and perfume balms, are widely popular due to their ease of use and long-lasting scent. The core of the user experience for these products lies in the controlled release of fragrance: they require a continuous and stable release of fragrance under normal conditions, while also aiming to enhance the fragrance intensity under specific conditions; at the same time, they must prevent product deterioration, rapid fragrance dissipation, or quality degradation caused by changes in environmental humidity or physical wear.

[0003] To achieve controlled aroma release, existing technologies often employ microencapsulation or polymer film coating. While microencapsulation technology can provide a certain degree of sustained release, the mechanical strength of its capsule walls is typically low, making them prone to rupture under friction or pressure. This results in a large, one-time release of aroma, failing to achieve long-lasting and intelligent release. Furthermore, the bonding strength between the microcapsule and the substrate is also a significant challenge.

[0004] On the other hand, surface coating with film-forming materials is another common method. For example, using a single cellulose acetate membrane or a polyurethane membrane. While cellulose acetate membranes have good breathability and film-forming properties, their moisture permeability is not sensitive enough to changes in external temperature, making it unable to achieve a smart fragrance release effect. More importantly, single cellulose acetate membranes have poor mechanical strength, abrasion resistance, and UV resistance, making them easily damaged by scratches during daily use or prone to aging and yellowing due to light exposure, affecting the product's appearance and function. While single polyurethane membranes are flexible and abrasion-resistant, they typically have poor breathability and lack selective permeability and smart response capabilities for fragrance molecules.

[0005] Furthermore, most existing coating films employ a single-layer structure with limited functionality. Simply blending materials with different functions into a single film often results in poor compatibility and mutual functional constraints. For example, inorganic molecules added to increase hardness may compromise the film's density, leading to decreased water resistance; while hydrophobic components may interfere with the normal permeation of fragrance molecules.

[0006] Therefore, there is an urgent need in this field for a novel composite membrane structure that can not only intelligently respond to ambient temperature and regulate the aroma release rate, but also possess excellent mechanical strength, wear resistance, weather resistance, and long-term stability to meet the comprehensive requirements of high-end solid fragrance products for coating materials. Summary of the Invention

[0007] The first objective of this invention is to provide a coating film comprising an inner coating liquid layer and an outer coating liquid layer, wherein the inner and outer coating liquid layers comprise the following components by weight:

[0008] Inner coating solution:

[0009] Temperature-sensitive grafted cyclodextrin, 15 parts

[0010] Cellulose acetate, 60 parts

[0011] Plasticizer, 10 parts

[0012] Hydrophobic nano-inorganic molecules, 5 parts;

[0013] Outer coating solution:

[0014] Waterborne polyurethane, 80 parts

[0015] Hardener, 8 parts

[0016] Fluorocarbon surface additive, 1 part

[0017] Crosslinking agent, 3 parts;

[0018] The temperature-sensitive grafted cyclodextrin is a cyclodextrin molecule co-grafted with poly(N-isopropylacrylamide) and branched alkyl groups;

[0019] The fluorocarbon surface additive is a compound with a perfluoroalkyl chain.

[0020] The thickness of the inner coating liquid on the substrate is at least 20 μm; the thickness of the outer coating liquid on the inner coating liquid is at least 40 μm.

[0021] Preferably, the method for preparing the temperature-sensitive grafted cyclodextrin includes the following steps:

[0022] S1: Brominated β-cyclodextrin, N-isopropylacrylamide monomer, catalyst and ligand are dissolved in an ethanol / water mixed solvent, and after deoxygenation, an atom transfer radical polymerization grafting reaction is carried out under inert gas protection to obtain poly(N-isopropylacrylamide) grafted cyclodextrin.

[0023] S2: Poly(N-isopropylacrylamide) grafted cyclodextrin is dissolved in a solvent, and an activator and branched alkyl bromide are added; after heating, a branched alkylation reaction occurs to obtain temperature-sensitive grafted cyclodextrin.

[0024] Preferably, the molar ratio of the branched alkyl group to the cyclodextrin core in the temperature-sensitive grafted cyclodextrin is 0.5-2.0:1.

[0025] Preferably, the number-average molecular weight of the poly(N-isopropylacrylamide) in the temperature-sensitive grafted cyclodextrin is 3500-6000 g / mol; the molar ratio of the poly(N-isopropylacrylamide) chain to the cyclodextrin is 5-12:1.

[0026] Preferably, the cellulose acetate is cellulose diacetate with a degree of substitution between 2.4 and 2.7.

[0027] Preferably, the plasticizer is a citrate ester plasticizer.

[0028] Preferably, the crosslinking agent is a blocked isocyanate.

[0029] Preferably, the hardener is a nanoscale metal oxide.

[0030] A second objective of this invention is to provide a method for preparing the aforementioned coated film, comprising the following steps:

[0031] S1: Add each component of the inner layer to the solvent one by one, then stir evenly and homogenize, let stand to remove bubbles and set aside for later use to obtain the inner layer coating solution;

[0032] S2: Plasma treatment is performed on the surface of the substrate to be coated, and then an inner coating liquid is sprayed onto the surface of the substrate to ensure that the thickness of the inner coating liquid on the substrate is at least 20μm; then heat curing is performed.

[0033] S3: Add all components of the outer layer except the crosslinking agent to the solvent, then stir and homogenize. After degassing, add the crosslinking agent and stir until homogenized before use to obtain the outer coating solution.

[0034] S4: After the inner coating on the substrate has cured and cooled, spray the outer coating liquid onto its surface to ensure that the thickness of the outer coating liquid on the substrate is at least 40μm; then heat to cure and activate the crosslinking reaction to obtain the coating film.

[0035] The third objective of this invention is to provide the application of the aforementioned coating film in encapsulating solid fragrance products, including but not limited to solid fragrance pastes, fragrance beads, and other solid products whose primary purpose is to emit fragrance.

[0036] This invention provides a double-layered coating film, the core principle of which lies in the synergistic solution to the technical challenges faced by compound incense beads through innovative molecular-level design and precise division of functional layers. The film comprises a function-oriented inner layer and a protective outer layer.

[0037] The inner layer is based on the core principle of intelligent controlled release. The key lies in the use of a specially formulated temperature-sensitive grafted cyclodextrin, prepared through a two-step synthesis: First, poly(N-isopropylacrylamide) segments are grafted onto the cyclodextrin using atom transfer radical polymerization. The reversible hydrophilic-hydrophobic phase transition of this polymer chain at a specific temperature (approximately 32-35°C) acts as a "molecular switch" regulating aroma release. Second, by introducing branched alkyl groups in a specific molar ratio, the cyclodextrin cavity is protected and hydrophobically modified. This effectively prevents the polymer chains from blocking the cavity at low temperatures and enhances the hydrophobic barrier properties of the entire inner membrane. The inner layer uses cellulose acetate as the film-forming matrix, ensuring basic adhesion and permeability of the membrane. Its working principle is as follows: At room temperature (below LCST), the poly(N-isopropylacrylamide) chains hydrophilically extend and form open hydrophilic diffusion channels together with cellulose acetate. At the same time, the cyclodextrin cavity can encapsulate aroma molecules, achieving stable and slow release of aroma. When the temperature rises to human skin temperature (above LCST), the polymer chains undergo a violent hydrophilic-hydrophobic transition and rapidly contract and collapse. This process physically closes or significantly compresses the previously formed hydrophilic channels, greatly increasing the diffusion resistance and path tortuosity of aroma molecules, thereby significantly reducing the release rate.

[0038] The outer layer's core principle is to construct a robust and durable protective barrier. It uses waterborne polyurethane as the continuous phase, shielding high-energy photons through its own components or added inorganic UV absorbers, thus protecting the inner layer and the fragrance beads from photodegradation at the source. Nanoscale hardeners (such as zirconium oxide) added to the outer layer act as rigid fillers, and their uniform dispersion within the polymer matrix significantly enhances the film's hardness, abrasion resistance, and scratch resistance. The contained fluorocarbon surface additives, with their extremely low surface energy due to their perfluoroalkyl chains, spontaneously migrate to the coating surface after film formation, creating a stable hydrophobic and oleophobic layer, giving the product excellent antifouling properties. The waterborne blocked isocyanate crosslinking agent used is unblocked during the final thermosetting stage. The released isocyanate groups chemically react with the active hydrogen sites on the polyurethane molecular chains, forming a stable three-dimensional network structure. This process fundamentally improves the outer film's water resistance, solvent resistance, and mechanical strength, and firmly locks its components within the network.

[0039] Compared with the prior art, the present invention has the following significant advantages and beneficial effects:

[0040] 1. Achieving intelligent temperature-controlled slow release and stable encapsulation

[0041] The inner membrane utilizes a specially formulated temperature-sensitive grafted cyclodextrin to achieve intelligent aroma regulation. At room temperature, the poly(N-isopropylacrylamide) chains hydrophilically extend, forming open channels. The cyclodextrin cavities effectively encapsulate aroma molecules, ensuring a long-lasting and stable release of the aroma. When the temperature rises to body temperature, the polymer chains hydrophobically contract, actively closing the aroma diffusion channels and significantly reducing the release rate. This effectively minimizes ineffective volatilization during wear, thereby greatly extending the overall lifespan of the fragrance beads. The introduced branched alkyl groups not only prevent the polymer chains from blocking the cavities at low temperatures but also enhance the overall hydrophobic barrier properties of the inner layer, further stabilizing the encapsulation and release process.

[0042] 2. Provides robust and weather-resistant all-around physical protection.

[0043] The outer membrane of this invention constructs a durable barrier through the synergistic effect of its components. The waterborne polyurethane matrix effectively blocks light, delaying the photoaging of the inner layer and the fragrance. Nanoscale hardeners (such as zirconium oxide) act as rigid fillers, significantly improving the membrane's hardness, abrasion resistance, and scratch resistance. Fluorocarbon surface additives form a low-surface-energy oleophobic and hydrophobic layer, giving the product excellent antifouling properties. Meanwhile, the blocked isocyanate crosslinking agent forms a three-dimensional network structure during thermosetting, greatly enhancing the outer membrane's water resistance, mechanical strength, and overall stability, effectively resisting daily physical friction and the erosion of complex environments.

[0044] 3. Achieve collaborative performance optimization through functional layering.

[0045] The dual-layer composite structure of this invention fundamentally solves the problem of limited functionality in single-layer membranes. The inner layer focuses on the intelligent recognition and controlled release of aroma molecules, while the outer layer focuses on resisting external environmental aggressors. Each layer performs its specific function, avoiding performance limitations. This design enables the product to simultaneously achieve high levels of performance in both "dynamic intelligent aroma release" and "long-lasting, robust protection," meeting the stringent requirements of high-end solid fragrance products for the comprehensive performance of coating materials, demonstrating significant application value.

[0046] Overall, this invention achieves synergistic performance optimization through a composite structure of an intelligent controlled-release inner layer and a robust protective outer layer. The inner layer, utilizing a specially formulated temperature-sensitive grafted cyclodextrin, enables stable fragrance release at room temperature and intelligent sustained release triggered by body temperature, achieving long-lasting fragrance by reducing ineffective wear during wear. The outer layer, through the synergistic effect of UV-shielding polyurethane, nano-curing agents, fluorocarbon additives, and cross-linking agents, constructs a durable barrier that combines high hardness, wear resistance, UV resistance, and hydrophobic and stain-resistant properties. This design integrates intelligent fragrance saving with long-lasting protection, effectively overcoming the limitations of traditional coating materials with their single function, and significantly improving the user experience and lifespan of solid fragrance products. Detailed Implementation

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0049] In the description of this invention, the term "for example" is used to mean "used as an example, illustration, or description." Any embodiment described as "for example" in this invention is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use the invention. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that the invention can be made without using these specific details. In other instances, well-known structures and processes will not be described in detail to avoid obscuring the description of the invention with unnecessary detail. Therefore, the invention is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed herein.

[0050] Unless otherwise specified, the experimental methods used in the specific implementation methods are all conventional methods, and the materials and reagents used are all commercially available unless otherwise specified.

[0051] In this invention, unless otherwise specified, "%" represents a percentage by mass; the raw materials and reagents used are all commercially available products.

[0052] The raw materials used in this invention are as follows:

[0053] Cellulose acetate is domestically produced diacetate with a degree of substitution between 2.4 and 2.7;

[0054] The hardener is nano-sized zirconium oxide powder particles;

[0055] The plasticizer is a citrate ester plasticizer, specifically triethyl citrate;

[0056] The crosslinking agent is a blocked isocyanate, specifically toluene diisocyanate;

[0057] Hydrophobic nano-inorganic molecules are hydrophobic nano-silica.

[0058] Waterborne polyurethane is a single-component aliphatic waterborne polyurethane;

[0059] The fluorocarbon surface additive is a fluorocarbon-modified polyacrylate;

[0060] The catalyst used in the preparation of temperature-sensitive grafted cyclodextrin is cuprous bromide, the ligand is PMDETA (N,N,N′,N″,N″-pentamethyldiethylenetriamine), and the activator is sodium hydride.

[0061] Example 1: Preparation of grafted cyclodextrin

[0062] (1) The molar ratio of branched alkyl groups to cyclodextrin core is 0.5:1; the molar ratio of poly(N-isopropylacrylamide) chain to cyclodextrin is 5:1; the number average molecular weight of poly(N-isopropylacrylamide) is 3500-6000 g / mol. The preparation of temperature-sensitive grafted cyclodextrin includes the following steps:

[0063] S1 Synthesis of Poly(N-isopropylacrylamide) Grafted Cyclodextrin:

[0064] Prepare a dry, large reactor with stirring and temperature control functions, and purge the air with nitrogen; add brominated β-cyclodextrin (degree of substitution 10.5), N-isopropylacrylamide monomer, cuprous bromide and ligand PMDETA in sequence; the molar ratio is 1:200:10.5:10.5;

[0065] Inject sufficient 75% (v / v) ethanol aqueous solvent and start stirring to dissolve or disperse the solid as much as possible.

[0066] The reaction system was subjected to a three-cycle process of "freezing-vacuuming-thawing" to ensure complete deoxygenation.

[0067] Under nitrogen protection, the reactor was heated to 70°C and stirred vigorously at this temperature for 6 hours.

[0068] After the reaction is complete, the reactor is cooled to room temperature and exposed to air to terminate the reaction.

[0069] The reaction solution was transferred to a subsequent purification device and passed through a large chromatography column (filled with neutral alumina) to remove the copper catalyst.

[0070] Collect the filtrate and purify it using ultrafiltration or large-scale dialysis systems to remove small molecule impurities.

[0071] Finally, by spray drying, a white poly(N-isopropylacrylamide) grafted cyclodextrin solid powder was obtained.

[0072] S2 branched alkylation reaction

[0073] In a dry, nitrogen-protected reactor, the solid powder of poly(N-isopropylacrylamide) grafted cyclodextrin, product S1, was added and dissolved in anhydrous dimethyl sulfoxide. 30 L of anhydrous dimethyl sulfoxide was used for every 1 mol of poly(N-isopropylacrylamide) grafted cyclodextrin.

[0074] Sodium hydride was added slowly and in batches as an activator while being cooled in an ice-water bath and stirred. 0.75 mol of sodium hydride was used for every 1 mol of poly(N-isopropylacrylamide) grafted cyclodextrin.

[0075] After adding the ingredients, remove the ice bath and let the reaction mixture be stirred at room temperature for 30 minutes.

[0076] 2-Ethylhexyl bromide is added slowly dropwise using a metering pump. 0.75 mol of 2-ethylhexyl bromide is used for every 1 mol of poly(N-isopropylacrylamide) grafted cyclodextrin.

[0077] After the addition is complete, the reaction mixture is heated to 60°C and stirred for 12 hours under nitrogen protection.

[0078] After the reaction is complete, the reaction solution is slowly poured into a large amount of ice water for quenching; the crude product is collected by centrifugation and redissolved in an appropriate amount of pure water.

[0079] Purification is performed using an ultrafiltration system to completely remove anhydrous dimethyl sulfoxide, salts, and unreacted reagents.

[0080] The final purified solution was spray-dried to obtain the product, temperature-sensitive grafted cyclodextrin.

[0081] (2) The molar ratio of branched alkyl groups to cyclodextrin core is 2:1; the molar ratio of poly(N-isopropylacrylamide) chain to cyclodextrin is 12:1; the preparation of temperature-sensitive grafted cyclodextrin with a number-average molecular weight of poly(N-isopropylacrylamide) of 3500-6000 g / mol includes the following steps:

[0082] S1 Synthesis of Poly(N-isopropylacrylamide) Grafted Cyclodextrin:

[0083] Prepare a dry, large reactor with stirring and temperature control functions, and purge the air with nitrogen; add brominated β-cyclodextrin (degree of substitution 10.5), N-isopropylacrylamide monomer, cuprous bromide and ligand PMDETA in sequence; the molar ratio is 1:480:12.6:12.6;

[0084] Inject sufficient 75% (v / v) ethanol aqueous solvent and start stirring to dissolve or disperse the solid as much as possible.

[0085] The reaction system was subjected to a three-cycle process of "freezing-vacuuming-thawing" to ensure complete deoxygenation.

[0086] Under nitrogen protection, the reactor was heated to 70°C and stirred vigorously for 8 hours at this temperature.

[0087] After the reaction is complete, the reactor is cooled to room temperature and exposed to air to terminate the reaction.

[0088] The reaction solution was transferred to a subsequent purification device and passed through a large chromatography column (filled with neutral alumina) to remove the copper catalyst.

[0089] Collect the filtrate and purify it using ultrafiltration or large-scale dialysis systems to remove small molecule impurities.

[0090] Finally, by spray drying, a white poly(N-isopropylacrylamide) grafted cyclodextrin solid powder was obtained.

[0091] S2 branched alkylation reaction

[0092] In a dry, nitrogen-protected reactor, the solid powder of poly(N-isopropylacrylamide) grafted cyclodextrin, product S1, was added and dissolved in anhydrous dimethyl sulfoxide. 50 L of anhydrous dimethyl sulfoxide was used for every 1 mol of poly(N-isopropylacrylamide) grafted cyclodextrin.

[0093] Sodium hydride was added slowly and in batches as an activator while being cooled in an ice-water bath and stirred. 4 mol of sodium hydride was used for every 1 mol of poly(N-isopropylacrylamide) grafted cyclodextrin.

[0094] After the addition of the ingredients is complete, remove the ice bath and allow the reaction mixture to be stirred at room temperature for 60 minutes to ensure that the hydroxyl groups are fully activated into sodium alkoxide.

[0095] 2-Ethylhexyl bromide is added slowly dropwise using a metering pump. 3 mol of 2-ethylhexyl bromide is used for every 1 mol of poly(N-isopropylacrylamide) grafted cyclodextrin.

[0096] After the addition is complete, the reaction mixture is heated to 70°C and stirred for 24 hours under nitrogen protection.

[0097] After the reaction is complete, the reaction solution is slowly poured into a large amount of ice water for quenching; the crude product is collected by centrifugation and redissolved in an appropriate amount of pure water.

[0098] Purification is performed using an ultrafiltration system to completely remove anhydrous dimethyl sulfoxide, salts, and unreacted reagents.

[0099] The final purified solution was spray-dried to obtain the product, temperature-sensitive grafted cyclodextrin.

[0100] (3) The preparation of a temperature-controlled grafted cyclodextrin with a poly(N-isopropylacrylamide) chain to cyclodextrin molar ratio of 5:1 and a poly(N-isopropylacrylamide) number-average molecular weight of 3500-6000 g / mol includes the following steps:

[0101] S1 Synthesis of Poly(N-isopropylacrylamide) Grafted Cyclodextrin:

[0102] Prepare a dry, large reactor with stirring and temperature control functions, and purge the air with nitrogen; add brominated β-cyclodextrin (degree of substitution 10.5), N-isopropylacrylamide monomer, cuprous bromide and ligand PMDETA in sequence; the molar ratio is 1:200:10.5:10.5;

[0103] Inject sufficient 75% (v / v) ethanol aqueous solvent and start stirring to dissolve or disperse the solid as much as possible.

[0104] The reaction system was subjected to a three-cycle process of "freezing-vacuuming-thawing" to ensure complete deoxygenation.

[0105] Under nitrogen protection, the reactor was heated to 70°C and stirred vigorously at this temperature for 6 hours.

[0106] After the reaction is complete, the reactor is cooled to room temperature and exposed to air to terminate the reaction.

[0107] The reaction solution was transferred to a subsequent purification device and passed through a large chromatography column (filled with neutral alumina) to remove the copper catalyst.

[0108] Collect the filtrate and purify it using ultrafiltration or large-scale dialysis systems to remove small molecule impurities.

[0109] Finally, by spray drying, a white crude product of poly(N-isopropylacrylamide) grafted cyclodextrin was obtained.

[0110] End-capping treatment of S2 poly(N-isopropylacrylamide) grafted cyclodextrin:

[0111] Under nitrogen protection, poly(N-isopropylacrylamide)-grafted cyclodextrin, tributyltin hydride, and azobisisobutyronitrile were dissolved in ethanol and heated to 80°C for 12 hours; the molar ratio of poly(N-isopropylacrylamide)-grafted cyclodextrin, tributyltin hydride, and azobisisobutyronitrile was 1:12:1.2; the amount of ethanol used was 50 L of ethanol per 1 mol of poly(N-isopropylacrylamide)-grafted cyclodextrin.

[0112] After the reaction was complete, most of the toluene was removed by concentration, and the product was then precipitated in a large amount of n-hexane. Repeated precipitation and washing were performed to thoroughly remove tin salt byproducts and residual tin reagents, followed by vacuum drying to obtain a temperature-controlled grafted cyclodextrin.

[0113] (4) Preparation of branched alkyl grafted cyclodextrin with a molar ratio of branched alkyl to cyclodextrin core of 0.5:1, comprising the following steps:

[0114] S1 Synthesis of Poly(N-isopropylacrylamide) Grafted Cyclodextrin:

[0115] S1 branched alkylation reaction:

[0116] Under nitrogen protection, β-cyclodextrin was dissolved in anhydrous dimethyl sulfoxide; sodium hydride was slowly added in portions under ice bath cooling, followed by stirring at room temperature for 1 hour; then 2-ethylhexyl bromide was slowly added. The molar ratio of β-cyclodextrin, sodium hydride, and 2-ethylhexyl bromide was 1:0.75:0.75.

[0117] The reaction mixture was heated to 60°C and stirred vigorously for 12 hours under nitrogen protection.

[0118] S2 purification:

[0119] After the reaction is complete, the reaction solution is slowly poured into a large amount of ice water for quenching; the crude product is collected by centrifugation and extracted with a large amount of acetone or ethanol using a Soxhlet extract; anhydrous dimethyl sulfoxide, salts and unreacted reagents are completely removed.

[0120] The final product was spray-dried to obtain branched alkyl grafted cyclodextrin.

[0121] Example 2: Coating experiment of the coating film

[0122] Using commercially available incense beads as the substrate, a coating film coating experiment was conducted on their surface, which included the following steps:

[0123] S1 Preprocessing:

[0124] Weigh each component according to the proportions in Table 1, where the unit is parts by mass; remove the fragrance powder and dust from the surface of the substrate with a soft brush; then place it in a plasma treatment device to activate the surface of the incense beads.

[0125] Preparation of S2 inner coating solution:

[0126] The components of the inner coating solution were added to N,N-dimethylformamide (DMF) in the following order: cellulose acetate, grafted cyclodextrin, triethyl citrate, and hydrophobic nano-silica. The mixture was mechanically stirred at room temperature until all components dissolved and mixed evenly. Then, it was homogenized using a high-speed homogenizer for 15 minutes to ensure that the nanoparticles were evenly dispersed and free from agglomeration. Finally, it was allowed to stand for degassing to obtain a clear and uniform inner coating solution for later use.

[0127] The solid content of the inner coating solution is controlled at approximately 15%.

[0128] S3 Inner Coating and Curing:

[0129] The plasma-treated incense beads are immediately transferred to a fluidized bed spraying device for spraying the inner coating solution. By controlling the spraying rate, time, and bead movement, a uniform and continuous inner film is formed on the surface of the incense beads, with a thickness of at least 20 μm after drying.

[0130] Transfer the sprayed incense beads to a drying oven and cure at 50°C for 45 minutes; ensure that the cellulose acetate film is cured.

[0131] Preparation of S4 outer coating solution:

[0132] Waterborne polyurethane, hardener, and fluorocarbon surface additives were added to deionized water and mechanically stirred for 2 hours to ensure thorough emulsification and mixing. The mixture was then homogenized at 1500 rpm for 5 minutes using a homogenizer and allowed to stand to remove bubbles, resulting in a pre-coating solution without crosslinking agents.

[0133] Before use, add a crosslinking agent to the outer coating solution preparation solution and stir rapidly for 5 minutes to obtain the outer coating solution.

[0134] S5 outer coating and final curing:

[0135] After the inner coating solution has completely cured and cooled to room temperature, the incense beads are placed back into the spraying equipment. The outer coating solution prepared in step S4 is then sprayed. By precisely controlling the process parameters, a uniform and complete outer film is formed on the surface of the inner film of the incense beads, with a thickness of at least 40 μm after drying.

[0136] The outer coating solution needs to be sprayed within 2 hours after preparation.

[0137] Place the coated incense beads in a drying oven and cure them using a stepped temperature increase method. First, cure at 60℃ for 20 minutes to allow the moisture to evaporate slowly, then increase the temperature to 70℃ and cure for 40 minutes.

[0138] After curing, the incense beads are naturally cooled at room temperature and aged in the dark for 24 hours to obtain incense beads coated with a thin film.

[0139] Table 1 Material ratio of coating film

[0140]

[0141] The serial numbers (1), (2), (3), and (4) of the grafted cyclodextrins in Table 1 correspond to and follow the different grafted cyclodextrins prepared by serial numbers (1), (2), (3), and (4) in Example 1.

[0142] In Table 1, sample number 6 only performs steps S1, S2, and S3, but not step S4; sample number 7 performs step S1 and then skips steps S2 and S3, proceeding directly to step S4.

[0143] Performance tests were conducted on incense beads coated with a film and on raw, unprocessed incense beads. The test items included: aroma release rate, water resistance, and scratch resistance.

[0144] (1) Aroma release rate: The aroma release rate at different temperatures was tested by detecting the content of VOCs (volatile organic compounds) in the environment using a photoionization detector (PID). Specific method steps include:

[0145] S1 Preprocessing:

[0146] All samples of the blended incense beads were equilibrated for 24 hours under standard temperature and humidity conditions (25℃, 50%RH).

[0147] The sealed chamber was repeatedly flushed with VOC-free air or nitrogen until the background concentration inside the chamber stabilized at a low value (<50 ppb) when measured by PID.

[0148] S2 Sample Placement and Accumulation:

[0149] Quickly place the individual incense beads into the clean, sealed chamber and immediately seal it tightly.

[0150] The entire sealed chamber was placed at the target test temperature (20°C and 32°C).

[0151] Allow VOCs to accumulate statically for 30 minutes.

[0152] S3 concentration measurement:

[0153] After the predetermined accumulation time is reached, the PID probe is inserted into the head space of the sealed chamber through the sampling port.

[0154] After the reading stabilizes (approximately 10-30 seconds), record the stable concentration value displayed by the PID; the results are shown in Table 2 below.

[0155] (2) Waterproofing: Waterproofing is tested by water pressure resistance test.

[0156] S1 sample preparation:

[0157] Carefully cut the incense bead in half with a sharp blade to expose the internal cross-section. Select one hemispherical half for testing.

[0158] The hemispherical bead is fixed to a specially designed fixture with the membrane side facing up, ensuring that the edge of the bead is completely sealed to the fixture with waterproof sealant, forming a test area that exposes only the membrane surface.

[0159] S2 test settings:

[0160] The prepared sample is clamped onto the testing instrument with one side of the membrane facing the direction of the applied water pressure.

[0161] According to the ISO 811-2018 water pressure test method and evaluation criteria, the test parameters are set as follows: water temperature is normal temperature, and pressurization rate is 6.0 kPa / min.

[0162] S3 was tested:

[0163] The instrument is started, and the water pressure begins to rise at a constant rate.

[0164] Observe the surface of the membrane. If water droplets are found to have seeped through in three different locations, stop the test immediately.

[0165] Record the pressure value displayed by the instrument at this time, which is the hydrostatic pressure resistance value of the sample; the results are shown in Table 2 below.

[0166] (3) Mechanical scratch resistance: The cross-cut test was used.

[0167] S1 Sample Preparation:

[0168] Select incense beads with a smooth surface and intact coating; embed the incense beads into the soft material to fix them in place.

[0169] S2 grid:

[0170] Hold the scribing tool perpendicular to the sample surface and apply even pressure in one stroke to cut six parallel slits into the film. The slits should penetrate the entire film layer to the substrate. Rotate the sample approximately 90° and repeat the above operation to create a grid-like scribing pattern.

[0171] S3 Adhesive Tape Application and Removal:

[0172] Gently sweep away any loose coating debris from the grid area with a soft brush.

[0173] Take a piece of tape and place its center portion over the grid. Rub it back and forth with your fingers to ensure the tape makes full contact with the coating. Within 60 seconds, grab one end of the tape and quickly tear it off at approximately a 60-degree angle.

[0174] S4 rating:

[0175] Observe the grid area under sufficient light.

[0176] The coating is rated based on the proportion of the area that has peeled off, in accordance with the standard chart.

[0177] Level 0: The cut edges are completely smooth, with no chips falling off (best).

[0178] Level 1: Detachment area ≤ 5%.

[0179] Level 2: The area of ​​detachment is 5-15%.

[0180] Level 3: The area of ​​detachment is 15-35%.

[0181] Level 4: The area of ​​detachment is 35-65%.

[0182] Level 5: Detachment area > 65% (worst).

[0183] The results are shown in Table 2.

[0184] Table 2 Performance test results of blended incense beads

[0185]

[0186] As can be seen from the results in Table 2, the performance differences between serial numbers 6 (inner layer only, no outer layer), 7 (outer layer only, no inner layer) and 1-5 (inner layer + outer layer) are essentially due to the structural and functional differences between "single membrane layer" and "composite membrane layer", which is the most critical influencing factor.

[0187] 1. Impact on waterproofing (resistance to hydrostatic pressure)

[0188] Serial numbers 1-5 (inner layer + outer layer): hydrostatic pressure resistance reaches 19-26 kPa, significantly higher than that of a single membrane layer. This is because the inner layer (cellulose acetate + grafted cyclodextrin) provides basic density, while the outer layer (waterborne polyurethane + zirconium oxide) provides a high-strength hydrophobic barrier. The two form a "dense + high-strength" composite waterproof structure, which can effectively resist water pressure penetration.

[0189] Item 6 (inner layer only): Its hydrostatic pressure resistance is only 5 kPa, which is 1 / 4 to 1 / 5 of that of items 1-5. The reason is that the inner layer relies solely on cellulose acetate for film formation and lacks the high-strength support of the outer waterborne polyurethane and the reinforcing effect of zirconium oxide. As a result, the membrane layer has weak water pressure resistance and is easily permeated.

[0190] Item 7 (outer layer only): hydrostatic pressure resistance 16 kPa, lower than items 1-5. The reason is that without an inner layer as a base coat, the outer layer is directly sprayed onto the substrate surface, resulting in insufficient adhesion between the film layer and the substrate (lacking the transition bonding of the inner layer), and the presence of micropores, leading to a decrease in waterproof performance.

[0191] 2. Impact on Adhesion Grade

[0192] Items 1-5 and 7 (including the outer layer): Adhesion is Grade 1 (Excellent). The waterborne polyurethane of the outer layer has strong adhesion to the plasma-activated substrate and can form an interfacial interlock with the inner layer, improving the overall adhesion of the film.

[0193] Serial No. 6 (no outer layer): Adhesion level 4 (very poor); When the inner cellulose acetate film is bonded to the substrate alone, it lacks the "anchoring" effect of the outer layer, and the film itself is brittle after curing, making it easy to fall off during cross-cut adhesion testing.

[0194] 3. Impact on aroma release (VOCs)

[0195] Samples 1-5 (inner layer + outer layer): VOCs at 20℃ were significantly lower than those of samples 6, 7 and the original sample. The inner layer grafted with cyclodextrin can adsorb aroma molecules through "encapsulation," while the outer layer of aqueous polyurethane membrane further blocks molecular penetration, thus reducing aroma release through a dual effect.

[0196] Item 6 (inner layer only): VOCs at 20℃ are higher than those in items 1-5. Only the inner layer is encapsulated, without an outer layer barrier, so some encapsulated aroma molecules will still be released from the pores of the inner membrane.

[0197] Serial No. 7 (outer layer only): 20℃ / 32℃ are the highest levels, close to the original sample. There is no inclusion effect of inner layer grafted cyclodextrin, the outer layer can only provide slight barrier, aroma molecules can easily be released through the outer membrane, and there is no temperature regulation ability (no decrease at 32℃).

[0198] All five are “inner layer + outer layer” structures. Their performance differences mainly come from the type of grafted cyclodextrin (presence or absence of temperature-sensitive groups, branch density, and end-capping treatment), which in particular affect the “temperature sensitivity of aroma release” and the density of the membrane layer.

[0199] Serial Number 1: Temperature-Sensitive Grafted Cyclodextrin. The key characteristic of this cyclodextrin is the presence of poly(N-isopropylacrylamide) (PNIPAM) chains (temperature-sensitive groups, low critical solution temperature (LCST) of approximately 32°C), with a molar ratio of branched alkyl groups to the cyclodextrin core of 0.5:1 (low branch density) and a molar ratio of PNIPAM chains to cyclodextrin of 5:1. The impact on performance is as follows: at 20°C, the PNIPAM chains are in a stretched state, resulting in relatively large membrane pores and moderate VOC release; at 32°C, the LCST of PNIPAM is reached, and chain segment contraction reduces membrane pores, significantly decreasing VOC release and demonstrating a clear temperature-sensitive controlled-release effect.

[0200] Serial No. 2: The temperature-sensitive grafted cyclodextrin type is exactly the same as Serial No. 1, but the amount of key inner layer components is increased, which leads to performance differences.

[0201] No. 3: Temperature-sensitive grafted cyclodextrin, but with higher branch density and PNIPAM chain content: the molar ratio of branched alkyl groups to the cyclodextrin core is 2:1 (4 times that of No. 1), and the molar ratio of PNIPAM chains to cyclodextrin is 12:1 (2.4 times that of No. 1). The higher branch density enhances the inclusion capacity of aroma molecules, and the VOCs release at 20℃ is lower than that of No. 1; the more PNIPAM chains shrink more significantly at 32℃, further reducing the membrane porosity, and the VOCs release drops to the lowest value at 32℃ in Table 2, showing the most prominent temperature-sensitive controlled release effect.

[0202] No. 4: Single-temperature-controlled grafted cyclodextrin. This cyclodextrin retains the PNIPAM temperature-sensitive chain (with the same PNIPAM chain molar ratio as No. 1, both being 5:1), but undergoes additional end-capping treatment—residual active groups at the ends of the PNIPAM chains are removed using tributyltin hydride and azobisisobutyronitrile. End-capping weakens the cyclodextrin's ability to encapsulate aroma molecules, resulting in the highest VOC release at 20℃ among Nos. 1-5; however, the PNIPAM temperature-sensitive chain is not destroyed and can still shrink normally at 32℃, reducing VOC release to the same level as No. 1, thus maintaining its temperature-controlled release function.

[0203] No. 5: Non-temperature-sensitive grafted cyclodextrin. The core characteristic of this cyclodextrin is the absence of the PNIPAM temperature-sensitive chain. It achieves the inclusion of aroma molecules solely through grafting of branched alkyl groups. The inclusion capacity of the branched alkyl groups is stable, and the VOCs release at 20°C is the lowest among Nos. 1-5. However, due to the absence of the PNIPAM temperature-sensitive chain, there is no chain segment contraction effect at 32°C, and the VOCs release remains the same as at 20°C, completely lacking temperature-sensitive controlled-release capability.

[0204] Because humans have extremely low olfactory thresholds for most fragrance molecules, such as santalol α with a threshold range of 0.01-0.1 ppb and muscone with a threshold range of 0.0001-0.001 ppb, which are basically in the ultra-trace range (0.001–0.1 ppb), even the encapsulated fragrance pills can function normally.

[0205] Furthermore, this invention releases aroma at a base rate at low temperatures, which decreases as the temperature rises. When the incense beads are left to stand (room temperature below 32°C), the molecular structure is in a hydrophilic, expanded state, forming open hydrophilic channels within the membrane, allowing the aroma to be released at a moderate base rate, maintaining a pleasant fragrance in the environment. When the incense beads are worn on the body (body temperature rises above 32°C), the temperature-sensitive molecular structure undergoes a drastic transformation, changing from hydrophilic to hydrophobic and contracting violently, actively closing most of the aroma diffusion channels.

[0206] This "heat-activated" characteristic enables a highly efficient "on-demand distribution" mechanism: when worn, it doesn't simply weaken the fragrance, but significantly reduces "excessive evaporation" and waste that travels far and is imperceptible to the wearer. Because the fragrance beads are in close contact with the body, very close to the olfactory senses, even at low release rates, a sufficient amount of fragrance molecules can still be clearly captured, ensuring that the close-range fragrance experience is unaffected. Therefore, this invention can greatly suppress the ineffective loss of fragrance without compromising the actual wearing experience, using every bit of fragrance effectively, thereby multiplying the effective lifespan of the fragrance beads and maximizing both long-lasting fragrance and economic benefits.

[0207] Another important point is the instant the temperature crosses the LCST (e.g., a rapid increase from 29°C to 33°C). At this moment, the previously swollen PNIPAM chains rapidly dehydrate and shrink. This rapid shrinkage process, like wringing out a towel, instantly squeezes out the water molecules and a small amount of dissolved aroma molecules that were trapped in the inter-chain water channels during swelling. This results in a very brief, sharp release peak. This is the burst of aroma that the wearer can clearly perceive, thus sensing the lifespan of the blended fragrance beads. Afterward, the PNIPAM chains have completed their shrinkage, transforming from stretched hydrophilic chains into dense hydrophobic clusters. The continuous, open hydrophilic diffusion channels previously provided for aroma molecules are disrupted and closed. The diffusion rate of aroma molecules in the hydrophobic, dense polymer clusters is extremely low. The diffusion path becomes longer and more tortuous. Under sustained, steady-state high-temperature conditions, the overall rate and flux of aroma molecules diffusing from the inside of the bead to the outside are significantly reduced; however, it is still perceptible to the human body.

[0208] Therefore, when we use a PID to measure the cumulative VOCs concentration after sufficient equilibration (30 minutes) at 32°C, we are measuring a significantly suppressed steady-state release dominated by the "channel closure" effect. Thus, the data clearly shows that the steady-state release rate at 32°C is much lower than that at 20°C.

[0209] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A coating film, characterized in that, The method for preparing the coating film includes the following steps: S1: The components of the inner coating solution are added to solvent A in the following order: cellulose acetate, temperature-sensitive grafted cyclodextrin, plasticizer, and hydrophobic nano silica. The mixture is then stirred evenly and homogenized. After standing to remove bubbles, the inner coating solution is ready for use. The inner coating solution comprises the following components by weight: 15 parts of temperature-sensitive grafted cyclodextrin 60 parts of cellulose acetate 10 parts plasticizer Five parts of hydrophobic nano-silica; S2: Plasma treatment is performed on the surface of the substrate to be coated, and then an inner coating liquid is sprayed onto the surface of the substrate to ensure that the thickness of the inner coating liquid on the substrate is at least 20μm; then heat curing is performed. S3: Add the waterborne polyurethane, hardener and fluorocarbon surface additive in the outer coating liquid to solvent B, then stir and homogenize. After degassing, add crosslinking agent and stir evenly before use to obtain the outer coating liquid. The outer coating solution comprises the following components by weight: 80 parts of waterborne polyurethane 8 parts hardener 1 part of fluorocarbon surface additive, 3 parts crosslinking agent; S4: After the inner coating liquid on the substrate has cured and cooled, spray the outer coating liquid onto its surface to ensure that the thickness of the outer coating liquid on the substrate is at least 40μm; then heat to cure and activate the crosslinking reaction to obtain the coating film; The temperature-sensitive grafted cyclodextrin is a cyclodextrin grafted with both poly(N-isopropylacrylamide) and branched alkyl groups; The fluorocarbon surface additive is a compound with a perfluoroalkyl chain; The preparation method of the temperature-sensitive grafted cyclodextrin includes the following steps: A1: Brominated β-cyclodextrin, N-isopropylacrylamide monomer, catalyst and ligand are dissolved in an ethanol / water mixed solvent, and after deoxygenation, an atom transfer radical polymerization grafting reaction is carried out under inert gas protection to obtain poly(N-isopropylacrylamide) grafted cyclodextrin. A2: Poly(N-isopropylacrylamide) grafted cyclodextrin is dissolved in solvent C, and an activator and branched alkyl bromide are added; after heating, a branched alkylation reaction occurs to obtain temperature-sensitive grafted cyclodextrin.

2. The coating film according to claim 1, characterized in that, The molar ratio of branched alkyl groups to the cyclodextrin core in the temperature-sensitive grafted cyclodextrin is 0.5-2.0:

1.

3. The coating film according to claim 1, characterized in that, The number-average molecular weight of the poly(N-isopropylacrylamide) in the temperature-sensitive grafted cyclodextrin is 3500-6000 g / mol; the molar ratio of poly(N-isopropylacrylamide) chain to cyclodextrin is 5-12:

1.

4. The coating film according to claim 1, characterized in that, The cellulose acetate is cellulose diacetate with a degree of substitution between 2.4 and 2.

7.

5. The coating film according to claim 1, characterized in that, The plasticizer is a citrate ester plasticizer.

6. The coating film according to claim 1, characterized in that, The crosslinking agent is a blocked isocyanate.

7. The coating film according to claim 1, characterized in that, The hardener is a nanoscale metal oxide.

8. The application of the coating film according to any one of claims 1-7 in the encapsulation of solid fragrance products.

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