A hydrothermal induction synergistic sunscreen cream and a preparation method thereof

Abstract

This invention provides a water- and heat-sensitive synergistic sunscreen and its preparation method, belonging to the field of cosmetic sunscreen technology. The sunscreen comprises a water-sensitive component, a heat-sensitive component, and a cosmetically acceptable carrier. The water-sensitive component includes zinc oxide particles and titanium dioxide particles with surfaces grafted with cellulose. The heat-sensitive component includes heat-responsive wax microcapsules with a melting point of 33°C to 38°C. When the sunscreen comes into contact with water or sweat, the cellulose-grafted inorganic particles rapidly densify the sunscreen film through hydrogen bonding between surface cellulose segments. When skin temperature rises, the heat-responsive wax microcapsules melt and fill the gaps in the film layers, further improving adhesion and sealing. The two components synergistically achieve a synergistic effect of increased density upon contact with water and enhanced adhesion upon contact with heat, improving the SPF value and achieving a higher SPF retention rate in water baths, while also providing a refreshing feel, excellent photostability, and system stability.

Description

Technical Field

[0001] This invention relates to the field of sunscreen preparation technology, specifically to a sunscreen with synergistic hydrothermal sensing effect and its preparation method. Background Technology

[0002] With the thinning of the atmospheric ozone layer and increased outdoor activities, the cumulative damage of ultraviolet (UV) radiation to the human body is becoming increasingly prominent, making sunscreen products an essential part of daily skin care. Currently, commercially available sunscreens primarily rely on a combination of physical and chemical sunscreens to block UV rays. Physical sunscreens, such as zinc oxide and titanium dioxide, work by reflecting and scattering UV rays, while chemical sunscreens, such as ethylhexyl methoxycinnamate and octocrylene, absorb UV rays and convert them into heat energy. Together, they can cover the entire UVA and UVB spectrum.

[0003] In recent years, some high-end products have adopted responsive sunscreen technologies, mainly divided into two categories. The first category is water-activated technology, exemplified by Shiseido's WetForce technology. This technology utilizes the sensitivity of mineral ion-sensing particles to moisture. When the sunscreen comes into contact with water or sweat, ionic cross-linking occurs between the components, forming a dense, waterproof sunscreen film, increasing its protective power by approximately 20% to 30% compared to its initial state. The second category is heat-activated technology, exemplified by Anessa's Thermo Booster technology. This technology uses heat-sensitive polymers that contract or expand when skin temperature rises, improving the adhesion of the sunscreen film to the skin. When the skin surface temperature reaches 37°C, the protective power can be increased by approximately 20%. Furthermore, Shiseido has integrated WetForce and HeatForce technologies into some products, but the two technologies function independently and have not formed a synergistic effect triggered by a single component within the same formulation system.

[0004] However, the industry has long faced the following core challenges: First, the single response and synergy are insufficient. Existing technologies can only achieve single enhancement when exposed to water or heat, and cannot achieve synergistic regulation of dual stimulation of water and heat in the same formula. In outdoor high temperature and high humidity scenarios, once the sunscreen film is damaged due to friction, water flow or thermal expansion and contraction, the protective power will be irreversibly reduced, and it cannot meet the long-term and stable protection needs.

[0005] Secondly, there is a significant contradiction between skin feel and protective power. To achieve a high SPF value, a high content of sunscreen agents is usually required, which makes the product oily, heavy, and prone to causing breakouts. Inorganic sunscreen particles are prone to agglomeration, resulting in an uneven sunscreen film, whitening, and a grainy feel.

[0006] The aforementioned problems severely restrict the promotion of sunscreen products in high-value-added application scenarios. The industry urgently needs a sunscreen production technology that can respond to both water and heat stimulation and has excellent skin feel and stability. Summary of the Invention

[0007] In view of this, the present invention provides a sunscreen with synergistic hydrothermal sensing effect and its preparation method, in order to solve the problems in the prior art where a single response mechanism cannot meet the protection needs of high temperature and high humidity complex scenarios, skin feel and stability are difficult to balance, and the system stability is poor.

[0008] To solve the above-mentioned technical problems, this invention constructs a "water-thermal dual-response synergistic network" to unify water-sensing components and heat-sensing components in the same formulation system, thereby endowing the sunscreen with the ability to trigger different response mechanisms sequentially or synergistically when stimulated by water and heat, and to simultaneously densify and fill gaps in the sunscreen film.

[0009] Its core working principle is as follows: The water-sensing component uses zinc oxide and titanium dioxide particles with cellulose grafted onto their surfaces as core functional particles. When the sunscreen comes into contact with water or sweat, the cellulose segments grafted onto the surface of the inorganic particles contain a large number of hydroxyl groups. A large number of intermolecular hydrogen bonds are rapidly formed between the cellulose molecules on the surfaces of adjacent particles, driving the sunscreen film to shrink towards a denser direction. The originally loosely porous areas in the film layer are compacted and closed, reducing the effective opening area of ​​the ultraviolet penetration path and significantly improving the protective power. The heat-sensing component uses heat-responsive wax microcapsules with a melting point of 33°C to 38°C as its core. This melting range is precisely matched with the range of temperature rise of the human body surface during sun exposure. When the skin temperature rises above the melting point of the microcapsules, the microcapsule walls melt and release molten phase change substances. These molten substances flow and spread along the gaps in the sunscreen film within the film layer, filling the voids formed by the accumulation of modified inorganic particles, further improving the sealing and skin adhesion of the sunscreen film, transforming the sunscreen film from a particle-stacking type film layer into a continuously filled dense film layer.

[0010] The hydrothermal synergistic mechanism is manifested as follows: water-stimulated hydrogen bond crosslinking is responsible for rapid densification and shrinking the membrane pore size; thermal stimulation-triggered microcapsule melting and filling is responsible for further sealing the residual gaps, upgrading the membrane from "densified" to "closed". The two can be superimposed in time and complement each other in effect, ultimately forming a synergistic effect of 1+1 greater than 2.

[0011] The sunscreen provided by this invention comprises a water-sensing component, a heat-sensing component, and a cosmetically acceptable carrier. The water-sensing component includes zinc oxide particles with a surface modified by cellulose grafting and titanium dioxide particles with a surface modified by cellulose grafting.

[0012] The preferred method for this cellulose grafting modification is as follows: zinc oxide particles and titanium dioxide particles are respectively aminated with a silane coupling agent, and then grafted onto cellulose activated with carbodiimide. The silane coupling agent introduces active amino groups onto the surface of the inorganic particles, while the carbodiimide-activated cellulose creates active sites on the cellulose molecular chains that can covalently bind with the amino groups, thereby achieving stable chemical grafting of cellulose molecules onto the surface of the inorganic particles. After modification, the particle size of the zinc oxide and titanium dioxide particles is preferably between 20 nm and 50 nm, balancing UV shielding efficiency and skin feel.

[0013] Furthermore, in the water-sensing component, the amount of zinc oxide particles with surface grafted with cellulose is preferably 5.0% to 12.0% of the total weight of the sunscreen, and the amount of titanium dioxide particles with surface grafted with cellulose is preferably 8.0% to 15.0%. The heat-sensing component includes heat-responsive wax microcapsules with a melting point of 33°C to 38°C, and the amount of these microcapsules is preferably 3.0% to 6.0% of the total weight of the sunscreen. The heat-responsive wax microcapsules preferably use paraffin wax as the core material and polysiloxane as the wall material, and can be prepared by interfacial polymerization or in-situ polymerization. They can maintain structural integrity under storage conditions and reliably melt and release the filler material within the temperature trigger range of the human body surface.

[0014] To further enhance sun protection capabilities, sunscreens may also contain at least one chemical sunscreen agent, preferably selected from ethylhexyl methoxycinnamate, hexyl diethylaminohydroxybenzoylbenzoate, octocrylene, and polysiloxane-15. These chemical sunscreen agents can work synergistically with physical sunscreen agents to achieve absorption and shielding of ultraviolet rays across the entire spectrum. Meanwhile, octocrylene can act as a photostable agent, delaying the photodegradation of other chemical sunscreen agents.

[0015] Furthermore, a cosmetically acceptable carrier is used to hold and disperse the aforementioned active ingredients, providing suitable spreadability, moisturizing properties, and stability. The carrier may contain oil-based components, water-based components, humectants, thickeners, and emulsifiers. The oil-based components may be selected from one or more of cyclopentasiloxane, diethylhexyl carbonate, squalane, jojoba esters, and cetyl ethylhexanoate, serving both as a solvent and dispersion medium for the sunscreen agent and imparting a smooth feel and water-repellent properties to the product.

[0016] Furthermore, the water-based components are mainly deionized water, and the moisturizers can be selected from glycerin, 1,3-propanediol, sodium hyaluronate, etc., which not only provide moisturizing effects, but also allow polyols such as glycerin to participate in hydrogen bond networks to help enhance the response sensitivity and cross-linking density of water-sensing components.

[0017] Furthermore, the thickener can be selected from acrylate cross-linked polymers to stabilize suspended inorganic particles and prevent sedimentation.

[0018] Furthermore, emulsifiers can be naturally provided through the emulsion structure formed by the appropriate ratio and process conditions of the oily and aqueous components in the system, or they can be added additionally. In addition, the carrier may also conventionally contain pH adjusters such as triethanolamine, preservatives such as a compound of phenoxyethanol and ethylhexylglycerin, antioxidants such as tocopheryl acetate, skin feel modifiers such as silica, and optional fragrances and other additives.

[0019] The preparation method of the sunscreen of the present invention includes the following steps: S1. Zinc oxide particles and titanium dioxide particles are respectively aminated using a silane coupling agent. Cellulose activated with carbodiimide is then grafted onto the aminated zinc oxide and titanium dioxide particles to obtain zinc oxide and titanium dioxide particles with cellulose grafting modification on their surfaces. The preferred reaction temperature for carbodiimide-activated cellulose is 40°C to 50°C, and the reaction time is 2 to 4 hours. The preferred amination treatment uses silane coupling agent KH-550 and reacts at room temperature for 1 to 2 hours. The preferred grafting reaction temperature is 60°C to 70°C, and the reaction time is 3 to 5 hours. After the reaction, the particles are washed with anhydrous ethanol and dried to obtain the modified powder.

[0020] S2. The modified zinc oxide particles, modified titanium dioxide particles, thermally responsive wax microcapsules, and oily components obtained in step 1 are mixed to form an oil phase, preferably dispersed at 75°C to 85°C at a rotation speed of 800 rpm to 1200 rpm until uniform and free of particles.

[0021] S3. Mix the aqueous components, humectant and thickener to form an aqueous phase, preferably at 75°C to 85°C until completely dissolved, the system is transparent and free of turbidity.

[0022] S4. Under stirring conditions, the oil phase is added to the aqueous phase for emulsification to obtain the sunscreen. Preferably, after adding the oil phase to the aqueous phase, it is first pre-emulsified at a speed of 1500 rpm to 2000 rpm for 5 to 8 minutes, then homogenized under high pressure at a pressure of 500 bar to 800 bar 2 to 3 times, then cooled to below 45°C, and pH adjuster and preservative are added. The mixture is then stirred evenly and discharged.

[0023] In summary, compared with the prior art, this application includes at least one of the following beneficial technical effects: 1. The hydrothermal synergistic sunscreen of this invention, upon contact with water or sweat, drives the densification of the sunscreen film through hydrogen bond cross-linking on the surface of cellulose grafted modified inorganic particles, thereby increasing the SPF value; when heated to 35°C to 40°C, the thermally responsive wax microcapsules melt and fill the gaps between the film layers, increasing the SPF value to 120% to 140% of the initial value; under the dual stimulation of water and heat, the SPF value stabilizes at more than 140% of the initial value, and the PA rating reaches PA++++, solving the problem of insufficient protection of existing single-response products in high temperature and high humidity composite scenarios.

[0024] 2. Excellent waterproof and sweat-resistant properties. The hydrogen bond cross-linking network formed by the cellulose graft layer can effectively lock the microstructure of the film layer, prevent the sunscreen agent from being washed away by water, improve the SPF retention rate and the adhesion of the sunscreen film after water bath, and eliminate the need for frequent reapplication, thus solving the problem of conventional sunscreens easily emulsifying and falling off when exposed to water and sweat.

[0025] 3. Refreshing and gentle on the skin. Cellulose grafting modification significantly improves the dispersibility of inorganic particles, allowing for rapid film formation after application. It has a matte texture, does not leave a white cast, and is non-greasy, resolving the contradiction of heavy skin feel in high SPF sunscreen products.

[0026] 4. Strong photostability. Through the synergistic effect of octocrylene's photoquenching and tocopheryl acetate's antioxidant free radical scavenging, it effectively inhibits the photodecomposition of chemical sunscreens, improves the retention rate of sun protection in simulated sunlight, and solves the problem of poor photostability of chemical sunscreens.

[0027] 5. Good system stability. The cellulose segments grafted onto the particle surface and the organosilane coupling agent together improve the compatibility of the organic-inorganic interface. Combined with the suspension effect of the thickener, the product shows no stratification or precipitation after 6 cycles of high and low temperature at 45℃ and -15℃, thus extending the shelf life of the sunscreen.

[0028] 6. The preparation process is highly industrially feasible. All modification steps and emulsification processes use common equipment and standardized operating procedures in the cosmetics industry. The parameters are precise and controllable, and the batch reproducibility is good, which can be directly realized on existing production lines for large-scale production. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the synergistic mechanism of water-heat induction in the sunscreen of the present invention; Figure 2 This is a flowchart illustrating the preparation process of the sunscreen according to the present invention.

[0030] Explanation of reference numerals in the attached figures: 100, water-sensing component; 200, heat-sensing component; 300, carrier. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described in detail below through embodiments. However, the embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention. All raw materials used are commercially available cosmetic or pharmaceutical grade products. Specific sources can be found with reference to commonly used industry suppliers. Cellulose was purchased from Shin-Etsu Chemical Co., Ltd. (Japan), carbodiimide from Sigma-Aldrich, silane coupling agent KH-550 from Nanjing Shuguang Chemical Group Co., Ltd., zinc oxide and titanium dioxide (20nm to 50nm) from Merck Group (Germany), ethylhexyl methoxycinnamate from BASF, and hexyl diethylaminohydroxybenzoyl benzoate from DSM. Octocrylene was purchased from BASF, polysiloxane-15 from Wacker Chemie, thermoresponsive wax microcapsules (melting point 33℃ to 38℃, paraffin core material, polysiloxane wall material) from Hangzhou Weimei Biotechnology Co., Ltd., cyclopentamethoxydimethylsiloxane from Dow Corning, diethylhexyl carbonate from Evonik, squalane from Nissin Olynyo Group of Japan, jojoba esters from Symrise, cetyl ethylhexanoate from Croda, and glycerol, 1,3-propanediol, acrylate crosspolymers (Carbopol Ultrez 21 polymer), triethanolamine, sodium hyaluronate, phenoxyethanol, ethylhexylglycerin, silica, tocopheryl acetate, and fragrances were all purchased from their respective well-known manufacturers.

[0032] like Figure 1 As shown, a water- and heat-sensing synergistic sunscreen comprises a water-sensing component 100, a heat-sensing component 200, and a cosmetically acceptable carrier 300. The water-sensing component 100 includes zinc oxide particles with a surface modified by cellulose grafting and titanium dioxide particles with a surface modified by cellulose grafting. The thermally responsive component 200 includes thermally responsive wax microcapsules with a melting point of 33°C to 38°C.

[0033] Cellulose grafting modification is prepared by amylating zinc oxide particles and titanium dioxide particles with silane coupling agents, and then grafting them with cellulose activated by carbodiimide.

[0034] Thermoresponsive wax microcapsules use paraffin as the core material and polysiloxane as the wall material.

[0035] The particle size of zinc oxide particles with cellulose grafting modification is 20 nm to 50 nm, and the particle size of titanium dioxide particles with cellulose grafting modification is 20 nm to 50 nm.

[0036] It also contains at least one chemical sunscreen agent selected from ethylhexyl methoxycinnamate, hexyl diethylaminohydroxybenzoyl benzoate, octocrylene, and polysiloxane-15.

[0037] The amount of heat-responsive wax microcapsules is 3.0% to 6.0% of the total weight of the sunscreen, the amount of zinc oxide particles with cellulose grafting modification on the surface is 5.0% to 12.0%, and the amount of titanium dioxide particles with cellulose grafting modification on the surface is 8.0% to 15.0%.

[0038] Cosmetic acceptable carriers 300 include oily ingredients, watery ingredients, moisturizers, thickeners, and emulsifiers.

[0039] like Figure 2 As shown, a method for preparing sunscreen includes the following steps: S1. Zinc oxide particles and titanium dioxide particles are respectively aminated using a silane coupling agent. Then, cellulose activated with carbodiimide is grafted onto the aminated zinc oxide and titanium dioxide particles to obtain zinc oxide and titanium dioxide particles with cellulose grafting modification on their surfaces. The reaction temperature for the carbodiimide-activated cellulose is 40°C to 50°C, and the reaction time is 2 to 4 hours. The amination treatment uses silane coupling agent KH-550 and reacts at room temperature for 1 to 2 hours. The grafting reaction temperature is 60°C to 70°C, and the reaction time is 3 to 5 hours. S2. The modified zinc oxide particles and modified titanium dioxide particles obtained in S1, thermally responsive wax microcapsules, and oily components are mixed to form an oil phase. S3. Mix the aqueous components, humectant, and thickener to form an aqueous phase; S4. The oil phase is added to the aqueous phase for emulsification to obtain sunscreen. Specifically, after the oil phase is added to the aqueous phase, it is pre-emulsified at a speed of 1500 rpm to 2000 rpm for 5 to 8 minutes, then homogenized under high pressure at a pressure of 500 bar to 800 bar 2 to 3 times, and then cooled and pH adjuster and preservative are added.

[0040] The sunscreen formula of this invention is divided into four main components according to function. The weight percentage range of each component is as follows. The formula ratio has been optimized through multiple experiments to achieve a balance between synergistic effects of water and heat and a good skin feel: 1. Hydrothermal sensing active components (35.0%–50.0%) Modified zinc oxide: 5.0%–12.0%, modified by CDI cellulose grafting, with a particle size of 20–50 nm, good dispersibility, strong UV blocking ability, and can effectively prevent agglomeration; Modified titanium dioxide: 8.0%–15.0%, modified with silane coupling agent + cellulose grafting to further enhance the UV blocking effect and improve compatibility with oil and water phases. Ethylhexyl methoxycinnamate: 4.0%–7.0%, a highly effective UVB absorber, which, when combined with other sunscreen agents, provides full-spectrum protection; Diethylaminohydroxybenzoyl benzoate: 1.0%–3.0%, a highly efficient UVA absorber that compensates for the shortcomings of inorganic sunscreens in UVA protection; Octocrylene: 2.0%–5.0%, with both UVB and UVA absorption capabilities, while also improving the photostability of other chemical sunscreens; Polysiloxane-15: 1.5%–3.5%, helps to enhance the thermal response effect and improve the smoothness and film formation speed of the sunscreen film; Thermally responsive wax microcapsules: 3.0%–6.0%, melting point 33–38℃. They melt upon heating to fill the gaps in the sunscreen film, improving adhesion. Their preparation can refer to the modification ideas of paraffin-based phase change microcapsules to ensure thermal stability and response sensitivity.

[0041] Oils and moisturizing components (20.0%–30.0%) Cyclopentadimethylsiloxane: 5.0%–10.0%, refreshing and non-greasy, improves product smoothness, and aids in the formation of sunscreen film; Diethylhexyl carbonate: 4.0%–8.0%, moisturizes the skin while enhancing the solubility of sunscreen agents and preventing particle aggregation; Squalane: 2.0%–5.0%, with good compatibility with human skin, moisturizing and hydrating, reducing the irritation of sunscreen agents on the skin; Jojoba esters: 1.0%–4.0%, enhance product moisturizing properties and improve waterproof performance; Cetyl ethylhexanoate: 3.0%–6.0%, lightweight and breathable, helps improve the stretchability of sunscreen film.

[0042] Aqueous phase and stabilizer (25.0%–40.0%) Deionized water: the remainder, used as a solvent in the system to ensure uniform dispersion of all components; Glycerin: 3.0%–8.0%, moisturizes and hydrates, while enhancing aqueous phase stability and assisting water-sensing component 100 in its function; 1,3-Propanediol: 2.0%–5.0%, which moisturizes while improving system compatibility and reducing stratification; Acrylic (ester) crosslinking polymer: 0.2%–0.8%, thickener and stabilizer, to ensure uniformity and stability of the system and prevent sunscreen agent sedimentation; Triethanolamine: 0.1%–0.5%, pH adjuster, adjusts the system pH to 5.5–7.0, which is close to the pH of human skin and reduces irritation; Sodium hyaluronate: 0.05%–0.2%, moisturizes and repairs, relieves skin dryness that may be caused by sunscreen; Phenoxyethanol / Ethylhexylglycerin: 0.5%–1.2%, a mild preservative that effectively inhibits microbial growth, extends product shelf life, and avoids the use of strong traditional preservatives.

[0043] Additives (0.5%–2.0%) Silica: 0.3%–1.0%, controls oil and absorbs sweat, reduces product greasiness, and enhances matte skin feel; Tocopheryl acetate: 0.2%–0.5%, an antioxidant that protects chemical sunscreens from oxidation and improves the photostability of the product; Fragrance: 0.1%–0.3% (optional), using hypoallergenic fragrances to improve product odor and enhance user experience.

[0044] The preparation method is as follows: The preparation method of this invention has clear steps and precise and controllable process parameters, which can effectively ensure product stability and hydrothermal synergy. The specific steps are as follows: Preparation of modified inorganic sunscreen CDI-activated cellulose: Take cellulose with a molecular weight of 50,000–2,500,000, add anhydrous DMF (N,N-dimethylformamide) as a solvent, stir evenly, add CDI (carbodiimide), and react at 40–50℃ for 2–4 hours to obtain an activated cellulose solution. The activation process requires strict control of temperature and time to ensure that the cellulose is fully activated, laying the foundation for subsequent grafting reactions.

[0045] Amination treatment of inorganic particles: Take zinc oxide and titanium dioxide powder, add silane coupling agent (preferably KH-550), stir evenly, and react at room temperature for 1-2 hours to introduce amino groups on the surface of inorganic particles, thereby enhancing their reactivity with activated cellulose. This step can effectively improve the dispersibility of inorganic particles and prevent subsequent agglomeration.

[0046] Grafting reaction: Aminated zinc oxide and titanium dioxide powders are slowly added to an activated cellulose solution, heated to 60–70℃, and reacted for 3–5 hours. After the reaction is completed, the powders are washed 3–4 times with anhydrous ethanol and then dried at 80–100℃ for 2–3 hours to obtain modified zinc oxide and modified titanium dioxide powders. The washing and drying steps can remove unreacted impurities and ensure the modification effect.

[0047] Oil phase preparation (A phase) In the oil phase pot, add cyclopentamethoxydimethylsiloxane, diethylhexyl carbonate, squalane, jojoba esters, cetyl ethylhexanoate (oil and moisturizing components), ethylhexyl methoxycinnamate, diethylaminohydroxybenzoylhexyl benzoate, octocrylene (chemical sunscreen), polysiloxane-15, and thermoresponsive wax microcapsules in sequence. Then add the modified zinc oxide and modified titanium dioxide powder prepared in step 1, as well as silica and tocopheryl acetate (some auxiliary agents). Heat the oil phase pot to 75–85°C, turn on the high-speed disperser, and disperse at a speed of 800–1200 rpm for 15–20 minutes until the system is uniform, free of particles and sediment, ensuring that all components are fully mixed and avoiding agglomeration of sunscreen agents.

[0048] Aqueous phase preparation (Phase B) In the aqueous phase pot, add deionized water, glycerin, 1,3-propanediol (moisturizing component), sodium hyaluronate, and acrylate cross-linking polymer (stabilizer) in sequence. Heat the aqueous phase pot to 75–85°C, turn on the stirrer, and stir at 300–500 rpm for 10–15 minutes until all components are completely dissolved and the system is clear and free of turbidity, ensuring the stability of the aqueous phase and avoiding subsequent emulsification and stratification.

[0049] Emulsification and Cooling Maintain the temperature of the aqueous phase (phase B) at 75–85℃. While stirring (500–800 rpm), slowly add the oil phase (phase A) to the aqueous phase (phase B). After the addition is complete, increase the speed to 1500–2000 rpm and pre-emulsify for 5–8 minutes to obtain a preliminary emulsified system. The feeding rate and stirring speed must be strictly controlled to avoid uneven emulsification.

[0050] The initial emulsification system is fed into a high-pressure homogenizer and homogenized 2–3 times at a pressure of 500–800 bar to obtain a fine and uniform emulsion. High-pressure homogenization can further refine the particles and improve the stability and skin feel of the system.

[0051] Transfer the homogenized emulsion to a cooling pot, turn on the stirrer, and allow it to cool naturally to below 45°C. Then add triethanolamine (pH adjuster), phenoxyethanol / ethylhexylglycerin (preservative), and fragrance (optional). Stir at 300–500 rpm for 30 minutes to ensure that all components are mixed evenly. Adjust the pH of the system to 5.5–7.0. The cooling rate should be controlled steadily to avoid sudden temperature drops that could cause the system to separate.

[0052] The uniformity and pH value of the emulsion are tested. Once the results are satisfactory, the emulsion is discharged, thus obtaining the hydrothermal synergistic sunscreen described in this invention.

[0053] Example 1 (Preferred Formula for Daily Outdoor Use) The recipe is as follows (based on a total weight of 100 grams): 8.0 g of cellulose-grafted zinc oxide particles (particle size 20 nm to 50 nm), 12.0 g of cellulose-grafted titanium dioxide particles (particle size 20 nm to 50 nm), 4.5 g of thermoresponsive wax microcapsules (melting point 33 °C to 38 °C), 5.5 g of ethylhexyl methoxycinnamate, 2.0 g of diethylaminohydroxybenzoylhexyl benzoate, 3.0 g of octocrylene, and polysiloxane-15 2.5g, cyclopentamethoxysiloxane 8.0g, diethylhexyl carbonate 6.0g, squalane 3.0g, jojoba esters 2.5g, cetyl ethylhexanoate 4.0g, glycerin 5.0g, 1,3-propanediol 3.5g, acrylate crosspolymer 0.5g, sodium hyaluronate 0.1g, silica 0.6g, tocopheryl acetate 0.3g, phenoxyethanol 0.6g, ethylhexylglycerin 0.2g, triethanolamine 0.3g, fragrance 0.2g, deionized water balance to 100g.

[0054] Preparation process: In the modification step, carbodiimide activated cellulose at 45℃ for 3 hours; zinc oxide and titanium dioxide were amination treated at room temperature for 2 hours using KH-550; the grafting reaction was carried out at 65℃ for 4 hours; the product was washed four times with anhydrous ethanol and dried at 90℃ for 2.5 hours to obtain the modified powder. Modified zinc oxide, modified titanium dioxide, thermally responsive wax microcapsules, chemical sunscreen, silica, tocopheryl acetate, and oily components were mixed and dispersed at 1000 rpm for 18 minutes at 80℃ to obtain the oil phase. Aqueous components, glycerin, 1,3-propanediol, sodium hyaluronate, and thickener were mixed and stirred at 80℃ for 12 minutes to obtain the transparent aqueous phase. Add the oil phase to the water phase while stirring at 600 rpm. After the addition is complete, increase the speed to 1800 rpm for pre-emulsification for 6 minutes. Then homogenize twice under high pressure at 600 bar. Allow to cool naturally to 40°C. Add triethanolamine, preservatives, and flavorings. Adjust the pH to 6.0. Stir until homogeneous and discharge.

[0055] Performance testing: SPF50+, PA++++; 92% SPF retention rate after 80-minute water bath; 35% increase in film density after 30 minutes of heating at 38℃; 88% retention rate of protective power after 12 hours of UV irradiation. It forms a film in 3 seconds upon application, with a matte finish that doesn't leave a white cast or feel greasy. No irritation or breakouts were observed in 30 volunteers after 28 days of use.

[0056] Example 2 (High Water Resistance Formula) The formula was adjusted as follows: 10.0 g modified zinc oxide, 14.0 g modified titanium dioxide, 5.5 g thermoresponsive wax microcapsules, 6.0 g ethylhexyl methoxycinnamate, 2.5 g diethylaminohydroxybenzoylhexyl benzoate, 4.0 g octocrylene, 3.0 g polysiloxane-15, 9.0 g cyclopentamethoxydimethylsiloxane, 7.0 g diethylhexyl carbonate, 2.5 g squalane, 3.0 g jojoba esters, 5.0 g cetyl ethylhexanoate, 4.0 g glycerin, 3.0 g 1,3-propanediol, 0.6 g acrylate crosspolymer, 0.1 g sodium hyaluronate, 0.8 g silica, 0.4 g tocopheryl acetate, 0.7 g phenoxyethanol, 0.3 g ethylhexylglycerin, 0.4 g triethanolamine, 0.2 g fragrance, and the balance being deionized water. The preparation process is the same as in Example 1, except that the high-pressure homogenization pressure is adjusted to 700 bar. Performance: SPF50+, PA++++; 95% SPF retention rate after 80 minutes of water bath; 40% increase in membrane density after heating at 38℃ for 30 minutes; 90% retention rate of protective power after 12 hours; refreshing feel, suitable for beach, swimming and other scenarios.

[0057] Comparative Example 1 (Ordinary sunscreen without cellulose grafting modification and without heat-responsive microcapsules) The modified particles were replaced with 10.0 g of unmodified ordinary zinc oxide and 10.0 g of ordinary titanium dioxide, non-thermal responsive wax microcapsules and polysiloxane-15, and the remaining components and processes were the same as in Example 1. Performance: SPF40, PA+++; 65% SPF retention after 80-minute water bath; significant film detachment after heating; oily and grainy feel on the skin; film formation takes more than 10 seconds; only 60% protective effect retention after 12 hours.

[0058] Comparative Example 2 (containing only water-sensing component 100, without thermal response component) The entire water-sensing component 100 and formulation of Example 1 were used, but the heat-responsive wax microcapsules and polysiloxane-15 were not used. Performance: The SPF increased to 118% after contact with water, confirming the water densification function of the cellulose grafted modified particles; however, the film densification did not change after heating, and there was no heat-responsive filling effect, indicating that the protective power under high temperature stimulation alone was not further improved when heat-sensing component 200 was missing.

[0059] Comparative Example 3 (containing only thermally responsive components, without anhydrous induction modifiers) The formulation uses 10.0g of unmodified zinc oxide and 10.0g of titanium dioxide, retains 4.5g of thermoresponsive wax microcapsules and 2.5g of polysiloxane-15, and does not add cellulose grafted modified particles. Performance: Upon contact with water, the SPF only increases to 102%, indicating almost no anhydrous densification effect; after heating at 38℃, the SPF increases to 118%, confirming the thermoresponsive filling function. However, due to uneven dispersion of inorganic particles, the basic protective strength is low, limiting the overall improvement.

[0060] As can be seen from the comparison of the examples and comparative examples, only by introducing inorganic particles with cellulose grafting modification on the surface and thermally responsive wax microcapsules with a melting point of 33°C to 38°C into the formula at the same time can the hydrothermal synergistic effect be obtained. Using either component alone cannot achieve the dual enhancement of protective power and long-term stability.

[0061] The experimental detection method is as follows: All performance data of this invention were obtained through the following standard testing methods, which comply with national cosmetic industry standards and internationally accepted standards, ensuring the data is authentic, reliable, and repeatable. The following parameters need to be tested: 1. SPF / PA value testing: The UV blocking ability of sunscreens is tested using an in vitro method (UV-2600 ultraviolet spectrophotometer) combined with a human method (according to ISO24444 international standard) to ensure accurate data.

[0062] 2. Waterproof performance test: In accordance with GB / T 29665-2013 "Cosmetic Safety Technical Specifications", an 80-minute water bath test was conducted to detect the change in SPF value before and after the water bath, calculate the retention rate, and evaluate the waterproof and sweat-resistant performance.

[0063] 3. Thermal response performance test: The sunscreen was applied to the surface of simulated skin and heated in a constant temperature environment of 38℃ for 30 minutes. The change in the density of the sunscreen film was observed under a microscope, and the change in SPF value was detected at the same time to evaluate the thermal response effect.

[0064] 4. System stability test: The sunscreen is placed in a high temperature environment of 45℃ and a low temperature environment of -15℃ for 6 cycles, each cycle lasting 24 hours. The product is observed to see if there are any phenomena such as layering, discoloration, or precipitation, and the stability of the system is evaluated.

[0065] 5. Skin feel and safety test: 30 volunteers (aged 18-45, including those with sensitive skin) were selected and used the sunscreen continuously for 28 days. The oiliness, film-forming speed and whitening of the product were evaluated. At the same time, the skin was observed for irritation reactions such as redness, stinging and breakouts. The evaluation results were recorded.

[0066] 6. Photostability test: The sunscreen was placed in a simulated ultraviolet irradiation environment (irradiation intensity simulated outdoor sun exposure) for 12 hours. The SPF / PA values ​​at different time points were measured, the retention rate was calculated, and the photostability was evaluated.

[0067] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0068] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A sunscreen with synergistic hydrothermal effect, characterized in that, It contains a water-sensing component (100), a heat-sensing component (200), and a cosmetically acceptable carrier (300); The water-sensing component (100) includes zinc oxide particles with cellulose grafting modification on the surface and titanium dioxide particles with cellulose grafting modification on the surface. The heat-sensitive component (200) comprises heat-responsive wax microcapsules with a melting point of 33°C to 38°C.

2. The sunscreen with synergistic hydrothermal effect as described in claim 1, characterized in that, The cellulose grafting modification is prepared by amylating zinc oxide particles and titanium dioxide particles with silane coupling agents, and then grafting them with cellulose activated by carbodiimide.

3. The sunscreen with synergistic hydrothermal effect as described in claim 1, characterized in that: The thermally responsive wax microcapsules use paraffin as the core material and polysiloxane as the wall material.

4. The sunscreen with synergistic hydrothermal effect as described in claim 1, characterized in that: The zinc oxide particles with surface grafted with cellulose have a particle size of 20 nm to 50 nm, and the titanium dioxide particles with surface grafted with cellulose have a particle size of 20 nm to 50 nm.

5. The sunscreen with synergistic hydrothermal effect as described in claim 1, characterized in that: It also contains at least one chemical sunscreen agent selected from ethylhexyl methoxycinnamate, hexyl diethylaminohydroxybenzoyl benzoate, octocrylene, and polysiloxane-15.

6. The sunscreen with synergistic hydrothermal effect as described in claim 1, characterized in that: The amount of the heat-responsive wax microcapsules is 3.0% to 6.0% of the total weight of the sunscreen, the amount of the zinc oxide particles with surface grafted with cellulose is 5.0% to 12.0%, and the amount of titanium dioxide particles with surface grafted with cellulose is 8.0% to 15.0%.

7. The sunscreen with synergistic hydrothermal effect as described in claim 1, characterized in that: The cosmetically acceptable carrier (300) comprises oily ingredients, aqueous ingredients, moisturizers, thickeners, and emulsifiers.

8. A method for preparing the sunscreen according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Zinc oxide particles and titanium dioxide particles are respectively aminated with silane coupling agent. Cellulose activated by carbodiimide is grafted onto the aminated zinc oxide particles and titanium dioxide particles to obtain zinc oxide particles and titanium dioxide particles with cellulose grafting modification on the surface. S2. The modified zinc oxide particles and modified titanium dioxide particles obtained in S1, thermally responsive wax microcapsules, and oily components are mixed to form an oil phase. S3. Mix the aqueous components, humectant, and thickener to form an aqueous phase; S4. The oil phase is added to the aqueous phase for emulsification to obtain the sunscreen.

9. The method for preparing the hydrothermal synergistic sunscreen as described in claim 8, characterized in that: In step S1, the reaction temperature of the carbodiimide-activated cellulose is 40°C to 50°C, and the reaction time is 2 to 4 hours; the amination treatment uses silane coupling agent KH-550 and reacts at room temperature for 1 to 2 hours; the grafting reaction temperature is 60°C to 70°C, and the reaction time is 3 to 5 hours.

10. The hydrothermal synergistic sunscreen and its preparation method as described in claim 8, characterized in that: In step S4, after the oil phase is added to the aqueous phase, it is pre-emulsified for 5 to 8 minutes at a speed of 1500 to 2000 rpm, then homogenized under high pressure 2 to 3 times at a pressure of 500 to 800 bar, and then cooled and pH adjuster and preservative are added.

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