High spf transparent sunscreen gel and method of making same

Abstract

The present application relates to the field of cosmetic formulation and preparation technology, and discloses a transparent sunscreen jelly with high SPF and a preparation method thereof, which comprises an A-phase component composed of deionized water, phenyl benzimidazole sulfonic acid, potassium hydroxide, a humectant, sodium chloride and a film-forming agent, a B-phase component composed of ethylhexyl salicylate, a silicone emulsifier, cyclopentasiloxane and a silicone elastomer prepolymer dispersion, and a C-phase component containing a preservative and a fragrance. In the preparation process, the A-phase and the B-phase are heated, mixed and homogenized, pulse homogenization is performed during the temperature reduction to the critical phase state locking temperature, and forced rapid cooling is performed. Through the cooperation of water-soluble sunscreen salts and oil-soluble sunscreen agents constrained by a silicone elastomer space grid, and the intervention of pulse shearing, the coalesced droplets are dispersed, the crystallization and stratification problem is effectively solved, and a sunscreen product with high SPF and long-term stable transparency is obtained.

Description

Technical Field

[0001] This invention relates to the field of cosmetic formulation and preparation technology, specifically to a high SPF transparent sunscreen gel and its preparation method. Background Technology

[0002] To achieve high SPF ratings, current sunscreen products typically require the addition of large amounts of physical and chemical sunscreen agents. This excessive addition can lead to solubility saturation in water-based formulas, causing sunscreen molecules to crystallize and precipitate. These solid crystals not only compromise the product's transparency but also result in uneven coating distribution on the skin. Furthermore, due to the difference in refractive indices between water-soluble and oil-soluble components, conventional mixing methods struggle to achieve refractive index balance at the interface, resulting in a cloudy appearance that fails to meet consumer demand for products with high SPF and uniform transparency.

[0003] In complex sunscreen systems, the dispersion stability of sunscreen agents within the matrix has always been a challenging issue in product development. Conventional products typically use simple polymeric thickeners to increase fluid viscosity in an attempt to prevent the aggregation of dispersed phase droplets. However, this simple physical thickening method is prone to irreversible damage to its internal structure under temperature changes and external mechanical shear forces. Due to the lack of a spatial cross-linked network structure that can intelligently respond to shear forces, the formulation is highly susceptible to the gradual separation of the aqueous and oil phases during long-term static storage. Furthermore, it lacks smooth rheological control during application and spread, resulting in a sticky feel on the skin.

[0004] Currently, when using traditional heating emulsification processes to prepare gel-based sunscreen products, there is a lack of precise control over the phase transition process during the cooling and curing stage. During the natural cooling process to the polymer network curing transition period, droplets dispersed within the system spontaneously undergo ripening, inevitably causing tiny droplets to coalesce into larger ones. Traditional processes fail to introduce appropriate mechanical interventions in the high-risk cooling temperature range, resulting in uneven distribution of microdroplet size within the network framework after it has solidified. Larger droplet sizes increase the scattering rate of light penetrating the coating, compromising the long-term physical stability of the gel network structure and leading to decreased product transparency. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high SPF transparent sunscreen gel and its preparation method, which solves the problems of existing sunscreen products easily crystallizing and precipitating when a large amount of sunscreen agent is added, resulting in a cloudy appearance; lack of spatial cross-linking network causing separation of water and oil phases during storage; and insufficient control of traditional cooling curing process leading to easy aggregation of dispersed droplets, resulting in increased light scattering and decreased transparency.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a high SPF transparent sunscreen gel, employing the following technical solution: A high SPF transparent sunscreen gel, by weight, comprises the following components: Phase A component for the aqueous base and water-soluble sunscreen phase: 50.85-75.25 parts deionized water; 1.0-3.0 parts phenylbenzimidazole sulfonic acid for the water-soluble sunscreen agent; 0.3-0.7 parts potassium hydroxide for the salt-forming agent; 2.5-5.5 parts 1,3-butanediol and 2.5-5.5 parts glycerol for the moisturizing agent; 0.5-1.0 parts sodium chloride for the stabilizer; and 0.5-1.5 parts an aqueous solution of vinylpyrrolidone / vinyl acetate copolymer for the aqueous film-forming agent; and components for the oil-based base and oil-soluble sunscreen phase. Phase B components: 2.0-5.0 parts of ethylhexyl salicylate for oil-soluble sunscreens, 1.0-2.0 parts of PEG-10 polydimethylsiloxane and 1.0-3.0 parts of polydimethylsiloxane PEG-10 / 15 crosspolymer for emulsifiers, 10.0-14.0 parts of cyclopentasiloxane for solvents, and 3.0-7.0 parts of silicone elastomer prepolymer dispersion for rheology modifiers; Phase C components for efficacy and modification phases: 0.05-0.15 parts of Stephania tetrandra extract, 0.05-0.15 parts of raspberry ketone glucoside, 0.3-0.5 parts of preservatives, and 0.05-0.15 parts of fragrance.

[0007] By employing the above technical solution, and through the combination of water-soluble and oil-soluble sunscreen components, along with a film-forming system and a rheology adjustment system, a transparent appearance with high sun protection capability and system stability is achieved. The specific microscopic mechanism and action are detailed below: In the initial stage of constructing the aqueous system, phenylbenzimidazole sulfonic acid in phase A undergoes an acid-base neutralization reaction under the action of potassium hydroxide, transforming from an acidic form into a water-soluble salt. Based on this ionization transformation process, the solubility limit of sunscreen molecules in deionized water is significantly increased, preventing crystallization due to concentration saturation in the formulation and maintaining the aqueous substrate in a single-phase transparent state. With the natural evaporation of water after application, the macromolecular segments of the vinylpyrrolidone / vinyl acetate copolymer dispersed within begin to interweave, forming a continuous polymeric physical film on the substrate surface. This structure effectively fixes the ionized sunscreen molecules within the film mesh, increasing the sunscreen coating's resistance to water washing.

[0008] Correspondingly, in the oil phase environment, the PEG-10 polydimethylsiloxane and the PEG-10 / 15 cross-linked polymer of polydimethylsiloxane in phase B are oriented at the interface between the two phases, reducing the interfacial tension between oil and water. Simultaneously, the silicone elastomer prepolymer dispersion introduced into the formulation undergoes macromolecular chain swelling in the cyclopentasiloxane environment, inducing a spatial volume expansion of the system. The swollen silicone elastomer prepolymer three-dimensional network interweaves and extends in the liquid system, constructing a steric barrier. The liquid oil-soluble sunscreen agent ethylhexyl salicylate is thus constrained within the spatial network of the silicone elastomer, limiting the aggregation and coalescence of oil droplets, allowing the refractive index at the two-phase interface to reach equilibrium, resulting in a macroscopically transparent gel state.

[0009] Preferably, the silicone elastomer prepolymer dispersion is obtained by the following preparation method: Under a protective atmosphere, 65.0-75.0 parts by weight of cyclopentamethoxysiloxane, 20.0-30.0 parts by weight of vinyl-terminated polydimethylsiloxane with a weight average molecular weight of 10,000-15,000 are mixed evenly as a matrix resin and 3.0-6.0 parts by weight of hydrogen-containing polydimethylsiloxane as a crosslinking agent; after heating to 60-65°C, isopropanol chloroplatinate solution is slowly added as a catalyst to induce hydrosilylation polymerization, and the system temperature is controlled to be maintained at 75-80°C for 2-3 hours; after the free Si-H bonds have completely reacted, the mixture is cooled to obtain the final product; wherein, the amount of isopropanol chloroplatinate solution is 5-15 ppm of the total mass of the matrix resin and crosslinking agent.

[0010] By employing the above technical solution, an elastomer dispersion exhibiting non-Newtonian fluid behavior was obtained through the polymerization and crosslinking of terminal vinyl polydimethylsiloxane with molecular weight and hydrogen-containing polydimethylsiloxane. The reaction mechanism mainly involves the following: In the specific crosslinking reaction, the carbon-carbon double bonds at the chain ends of the terminal vinyl polydimethylsiloxane in the matrix resin, under a protective atmosphere and heating environment, undergo electron cloud polarization under the coordination induction of the catalyst. After polarization, the silane-hydrogen bonds on the hydrogen-containing polydimethylsiloxane chain break, and hydrogen and silicon atoms respectively add to the adjacent carbon atoms of the polarized carbon-carbon double bonds, initiating a hydrosilylation reaction.

[0011] As the hydrosilylation reaction continues, the linear molecular chains of the matrix resin are chemically bonded together by a crosslinking agent. To avoid the formation of solid agglomerates due to excessively rapid local reactions, the system temperature is controlled at 75-80℃ during the process, promoting the uniform extension of polymer chains in the cyclopentamethoxysiloxane solvent and forming moderately crosslinked spatial network nodes. The reaction terminates once the free silane bonds in the system are consumed. The resulting spatially crosslinked polymer is uniformly dispersed in cyclopentamethoxysiloxane. When introduced into a sunscreen formulation, this structure deforms under mechanical shear force, causing a decrease in viscosity. Upon resting, the network recovers, causing a rebound in viscosity, thus giving the sunscreen gel flow control capabilities.

[0012] Secondly, the present invention provides a method for preparing a high SPF transparent sunscreen gel, using the following technical solution: A method for preparing a high SPF transparent sunscreen gel includes the following steps: Deionized water and phenylbenzimidazole sulfonic acid are mixed in a prescribed amount and stirred. Deionized water containing dissolved potassium hydroxide is added, and the pH of the system is adjusted to neutral. Subsequently, 1,3-butanediol, glycerol, sodium chloride, and an aqueous solution of vinylpyrrolidone / vinyl acetate copolymer are added sequentially, stirred, and heated to obtain a homogeneous and transparent A-phase component solution, which is then kept at this temperature for later use. Ethylhexyl salicylate, PEG-10 polydimethylsiloxane, polydimethylsiloxane PEG-10 / 15 crosspolymer, cyclopentamethoxysiloxane, and a silicone elastomer prepolymer dispersion are sequentially added to a main emulsifying vessel. A closed stirring system is activated, and the mixture is heated to a low speed until homogeneous, yielding a B-phase component for later use. While maintaining the temperature of the main vessel, a homogenizer is activated, and the A-phase component, which is at the same temperature as the B-phase component, is added. The solution was slowly and uniformly added to phase B under negative pressure to maintain homogeneity. After emulsification, the mixture was kept at a constant temperature, and then the heating was turned off, allowing for initial cooling at a natural cooling rate. During the cooling process, the material temperature was continuously monitored. When the system temperature dropped to the critical phase lock-in temperature, i.e., the temperature at which the polymer network of the system underwent solidification transformation, a pulse homogenization program was immediately initiated. Simultaneously with pulse homogenization, forced cooling water was activated to rapidly cool the system at a set forced cooling rate. Once the system was cooled to the temperature at which the active ingredient was added using forced cooling, pre-dissolved and mixed Stephania tetrandra extract and raspberry ketone glucoside solution, preservatives, and fragrances were added sequentially. The wall-scraping agitator was activated for mixing. At the same time, the main pot was vacuum-degassed. After the system was further cooled to the discharge temperature, the vacuum was released, and the mixture was filtered before being discharged to obtain the target high SPF transparent sunscreen gel.

[0013] By employing the above technical solution, and through isothermal mixing within a temperature range and staged cooling and homogenization control, stable solidification of the oil-water dispersion phase and uniformity of the system's refractive index are achieved. The specific reaction mechanism and process action mechanism are integrated throughout each stage: In phase A preparation, phenylbenzimidazole sulfonic acid particles dissociate in the alkaline environment provided by potassium hydroxide, resulting in proton transfer and the formation of water-soluble salts. The heating process intensifies molecular thermal motion, leading to a homogeneous thermodynamic dissolution state between the water-soluble matrix and polymer macromolecules in the aqueous phase. Moving to phase B preparation, the three-dimensional cross-linked network of the silicone elastomer prepolymer swells in the cyclopentamethoxysiloxane solvent. The enclosed heating state promotes the uniform insertion of oil-soluble sunscreen agents and surfactant molecules into the elastomer network structure, forming a uniformly viscous oil-based continuous phase.

[0014] Once the two phases are prepared and enter the high-temperature initial emulsification stage, the A-phase component solution enters the B-phase at the same temperature at a controlled rate under negative pressure, avoiding localized precipitation caused by the temperature difference between the two phases. The mechanical shear force of the homogenizer overcomes the surface tension of the droplets, breaking the aqueous phase into dispersed microdroplets. Under the action of mechanical force, the polyether-modified siloxane emulsifier molecules migrate towards the oil-water interface and are directionally adsorbed at the interface. The hydrophilic end extends into the interior of the microdroplets, and the silicate end extends into the continuous phase, initially establishing a phase interface barrier.

[0015] The subsequent cooling and curing process is the core technology for ensuring product transparency. During the initial cooling to the critical phase-locking temperature, the rheological characteristics of the system change, and the mobility of the polymer chains decreases. At this point, pulsed mechanical homogenization is introduced to disrupt the droplet aggregates initially formed during cooling. Combined with a forced cooling rate, this rapidly crosses the high-risk temperature range for aggregation, locking the particle size and distribution of the dispersed droplets at a kinetic level, forming a stable gel network structure and minimizing light scattering. In the final stages of adding active ingredients and degassing, the lower system temperature prevents the degradation or denaturation of heat-sensitive plant extracts. Vacuuming allows tiny gases introduced during emulsification and stirring to migrate to the liquid surface and be expelled, eliminating refractive index differences and total internal reflection caused by bubbles, thus achieving a uniform and transparent macroscopic product appearance.

[0016] Preferably, the temperature for stirring and heating and the temperature for opening and closing the stirring and heating are both 80-90℃; the pH value of the system is adjusted to neutral, and the pH value of the system is adjusted to 6.0-8.0; the stirring and heating are carried out to obtain a uniform and transparent A phase component solution, and the stirring speed is set to 300-400 r / min.

[0017] By employing the above technical solutions, maintaining a temperature environment of 80-90℃ provides the molecular activation energy required for the miscibility of the system components, promoting the complete expansion of the polymer film-forming agent and silicone elastomer chain segments. Controlling the pH value within the range of 6.0-8.0 ensures that the sunscreen agent remains in an ionized state. The set stirring speed provides the convective mass transfer power required for mixing, while avoiding the formation of strong vortices on the liquid surface that could entrain excessive air.

[0018] Preferably, the homogenizer is turned on, and the homogenization frequency is set to 40-50Hz, maintaining the homogenization conditions for 5-10 minutes; after emulsification, the system is kept at a constant temperature for 15-30 minutes; when the system temperature drops to the critical phase lock-in temperature, which is 50-60℃; the pulse homogenization program is operated by homogenizing at a frequency of 40-50Hz for 30-60 seconds, then pausing for 1-2 minutes, and repeating this cycle 3-5 times; forced cooling water is turned on to rapidly cool the system at a set forced cooling rate of 3-5℃ / min.

[0019] By employing the above-mentioned technical solution, the combination of emulsification homogenization frequency and time inputs appropriate mechanical energy into the fluid, pulverizing the dispersed phase to a specific particle size distribution. Based on this, the isothermal holding process provides adsorption equilibrium time for surfactant molecules at the nascent interface, reducing interfacial free energy. The critical phase-locking temperature is selected at 50-60℃ because the polymer network is in its curing transition phase at this temperature. An intermittent pulsed homogenization mechanism is used, alternating between applying shear force to disperse large droplets and allowing the elastic network structure to self-repair, coupled with forced heat removal at 3-5℃ / min. This promotes rapid shaping of the network framework within a state containing uniform microdroplets, interrupting the thermodynamic path of Oswald ripening of the droplets and establishing long-term physical stability.

[0020] Preferably, when the system is cooled to the temperature of the active ingredient by forced cooling, the temperature of the active ingredient is 39-45℃; during the vacuum degassing treatment of the main pot, the vacuum degree of the vacuum degassing treatment is controlled within the range of -0.08 to -0.05MPa; during the mixing process, the wall scraper is turned on and the speed of the wall scraper is set to 20-30r / min, and the mixing time is 10-15min; the discharge temperature is 30-35℃.

[0021] By employing the above technical solution, the addition temperature range of 39-45℃ avoids the thermal degradation threshold of the active ingredients. A set vacuum gradient establishes an internal and external pressure difference, causing the gas encapsulated within the high-viscosity network to overcome viscous resistance and escape. After degassing, low-speed wall-scraping stirring is used to achieve macroscopically uniform mixing of the added components without damaging the established physical nodes of the polymer gel network. Finally, the material is discharged at 30-35℃, maintaining the integrity of the gel structure.

[0022] This invention provides a high SPF transparent sunscreen gel and its preparation method. It has the following beneficial effects: 1. This invention converts phenylbenzimidazole sulfonic acid into a water-soluble salt under the action of an alkaline neutralizing agent, combines it with the liquid oil-soluble sunscreen agent ethylhexyl salicylate, and confines the ethylhexyl salicylate within the spatial network formed after the silicone elastomer prepolymer swells. This mechanism improves the solubility limit of the sunscreen molecules in deionized water, prevents the crystallization of large molecules, limits the aggregation and coalescence of oil droplets, and achieves a balance in the refractive index of the two-phase interface, thereby obtaining a sunscreen product with high sun protection capability and a macroscopically uniform and transparent appearance.

[0023] 2. This invention involves polymerizing and crosslinking vinyl-terminated polydimethylsiloxane with hydrogen-containing polydimethylsiloxane, causing polymer segments to extend uniformly in the cyclopentamethoxysiloxane solvent and form moderately crosslinked spatial network nodes. This structure avoids the formation of solid lumps due to excessively rapid local reactions. The resulting spatially crosslinked polymer undergoes network deformation under mechanical shear force, leading to a decrease in viscosity. Upon resting, the network recovers, causing the viscosity to rise again. This imparts flow control to the sunscreen gel and prevents stratification in the water-oil system.

[0024] 3. This invention introduces a pulsed homogenization process during the system's cooling to the critical phase lock-in temperature stage, combined with a set forced cooling rate to rapidly cool the material. The intermittently applied homogenous shear force can break up the droplet aggregates initially generated during the cooling process when the polymer network is in the curing transition period. Combined with the forced cooling action that rapidly removes heat, it promotes the rapid shaping of the network skeleton in a state containing uniform microdroplets, cuts off the thermodynamic path of droplet maturation, establishes long-term physical stability, and ensures that the scattering rate when light passes through is reduced to a minimum. Attached Figure Description

[0025] Figure 1 Rheological dynamic strain scanning curves of embodiments and comparative examples of the present invention; Figure 2 Visible light transmittance spectrum curves for embodiments and comparative examples of the present invention; Figure 3 The extreme stability water separation rate distribution trajectory diagrams of the embodiments and comparative examples of the present invention; Figure 4 This is a dual Y-axis trend graph showing the in vitro SPF and film-forming variation coefficient for embodiments and comparative examples of the present invention; Figure 5 This is a multi-dimensional line graph comparing the sensory evaluation of embodiments and comparative examples of the present invention. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0027] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing a silicone elastomer prepolymer dispersion, including the following steps: In a dry three-necked flask equipped with a stirrer and condenser, 70.0 parts by weight of cyclopentamethoxydimethylsiloxane were added as a reaction solvent, followed by 25.0 parts by weight of vinyl-terminated polydimethylsiloxane with a weight average molecular weight of 10,000 as the matrix resin, and 5.0 parts by weight of hydrogen-containing polydimethylsiloxane as a crosslinking agent. Under a nitrogen atmosphere, stirring was started and the system was heated to 60°C. A solution of isopropanol chloroplatinate, equivalent to 10 ppm of the total mass of the matrix resin and crosslinking agent, was slowly added as a catalyst. As the system underwent an exothermic hydrosilylation reaction, the temperature was strictly controlled and maintained at 75°C for crosslinking polymerization. The reaction was continued at this temperature for 2 hours. The reaction system was monitored in real time using an infrared spectrometer. When the infrared spectrum showed a value at 2160 cm⁻¹... -1 When the characteristic absorption peaks of the free Si-H bonds completely disappear, and the system exhibits a significant increase in viscosity and non-Newtonian fluid characteristics, the reaction is confirmed to be complete, and heating is stopped. The resulting reaction mixture is allowed to cool naturally to room temperature, yielding a semi-transparent gel-like dispersion of the silicone elastomer prepolymer.

[0028] Preparation Example 2: This preparation example provides a method for preparing a silicone elastomer prepolymer dispersion, including the following steps: In a dry three-necked flask equipped with a stirrer and condenser, 70.0 parts by weight of cyclopentamethoxydimethylsiloxane were added as a reaction solvent, followed by 25.0 parts by weight of vinyl-terminated polydimethylsiloxane with a weight average molecular weight of 12,500 as the matrix resin, and 5.0 parts by weight of hydrogen-containing polydimethylsiloxane as a crosslinking agent. Under a nitrogen atmosphere, stirring was started and the system was heated to 62°C. A solution of isopropanol chloroplatinate, equivalent to 10 ppm of the total mass of the matrix resin and crosslinking agent, was slowly added as a catalyst. As the system underwent an exothermic hydrosilylation reaction, the temperature was strictly controlled and maintained at 78°C for crosslinking polymerization. The reaction was continued at this temperature for 2.5 hours. The reaction system was monitored in real time using an infrared spectrometer. When the infrared spectrum showed a value at 2160 cm⁻¹... -1 When the characteristic absorption peaks of the free Si-H bonds completely disappear, and the system exhibits a significant increase in viscosity and non-Newtonian fluid characteristics, the reaction is confirmed to be complete, and heating is stopped. The resulting reaction mixture is allowed to cool naturally to room temperature, yielding a semi-transparent gel-like dispersion of the silicone elastomer prepolymer.

[0029] Preparation Example 3: This preparation example provides a method for preparing a silicone elastomer prepolymer dispersion, including the following steps: In a dry three-necked flask equipped with a stirrer and condenser, 70.0 parts by weight of cyclopentamethoxydimethylsiloxane were added as a reaction solvent, followed by 25.0 parts by weight of vinyl-terminated polydimethylsiloxane with a weight average molecular weight of 15,000 as the matrix resin, and 5.0 parts by weight of hydrogen-containing polydimethylsiloxane as a crosslinking agent. Under a nitrogen atmosphere, stirring was started and the system was heated to 65°C. A solution of isopropanol chloroplatinate, equivalent to 10 ppm of the total mass of the matrix resin and crosslinking agent, was slowly added as a catalyst. As the system underwent an exothermic hydrosilylation reaction, the temperature was strictly controlled and maintained at 80°C for crosslinking polymerization. The reaction was continued at this temperature for 3 hours. The reaction system was monitored in real time using an infrared spectrometer. When the infrared spectrum reached 2160 cm⁻¹... -1 When the characteristic absorption peaks of the free Si-H bonds completely disappear, and the system exhibits a significant increase in viscosity and non-Newtonian fluid characteristics, the reaction is confirmed to be complete, and heating is stopped. The resulting reaction mixture is allowed to cool naturally to room temperature, yielding a semi-transparent gel-like dispersion of the silicone elastomer prepolymer.

[0030] Examples 1-3:

[0031] Example 1: This embodiment provides a high SPF transparent sunscreen gel and its preparation method. The composition, by weight, consists of the following components: Phase A: 75.25 parts by weight of deionized water, 1.0 part by weight of phenylbenzimidazole sulfonic acid, 0.3 parts by weight of potassium hydroxide, 2.5 parts by weight of 1,3-butanediol, 2.5 parts by weight of glycerol, 0.5 parts by weight of sodium chloride, and 0.5 parts by weight of an aqueous solution of vinylpyrrolidone / vinyl acetate copolymer (VP / VA copolymer 73W). Phase B: 2.0 parts by weight of ethylhexyl salicylate, 1.0 part by weight of PEG-10 polydimethylsiloxane, 1.0 part by weight of polydimethylsiloxane PEG-10 / 15 crosslinked polymer, 10.0 parts by weight of cyclopentadimethylsiloxane, and 3.0 parts by weight of the silicone elastomer prepolymer dispersion obtained in Preparation Example 1; Phase C: 0.05 parts by weight of Stephania tetrandra extract, 0.05 parts by weight of raspberry ketone glucoside, 0.3 parts by weight of preservative (phenoxyethanol and ethylhexylglycerin in a conventional ratio), and 0.05 parts by weight of fragrance.

[0032] Its preparation method includes the following steps: Step 1: Preparation of Phase A Most of the deionized water and 1.0 part by weight of phenylbenzimidazole sulfonic acid were added to an aqueous reaction vessel and stirred. 0.3 parts by weight of potassium hydroxide were dissolved in a small amount of reserved deionized water and then slowly added dropwise to the system under close monitoring. The pH of the system was precisely adjusted to 7.0 to ensure complete salt dissolution of the sunscreen agent and a clear, crystal-free system. Subsequently, 2.5 parts by weight of 1,3-butanediol, 2.5 parts by weight of glycerol, 0.5 parts by weight of sodium chloride, and 0.5 parts by weight of an aqueous solution of vinylpyrrolidone / vinyl acetate copolymer were added sequentially. The mixture was stirred at 300 rpm and heated to 80°C to form a homogeneous and transparent phase A solution, which was then kept at this temperature for later use.

[0033] Step 2: Preparation of Phase B 2.0 parts by weight of ethylhexyl salicylate, 1.0 parts by weight of PEG-10 polydimethylsiloxane, 1.0 parts by weight of polydimethylsiloxane PEG-10 / 15 crosspolymer, 10.0 parts by weight of cyclopentamethoxydimethylsiloxane, and 3.0 parts by weight of the silicone elastomer prepolymer dispersion synthesized in Preparation Example 1 were sequentially added to the main emulsifying vessel. A closed stirring was turned on, and the mixture was heated to 80°C and mixed at low speed until homogeneous.

[0034] Step 3: High-temperature initial emulsification Maintain the main pot temperature at 80℃, turn on the homogenizer, and set the homogenization frequency to 40Hz. Slowly and uniformly add phase A (80℃) to phase B under negative pressure. Maintain this temperature and homogenization conditions for 5 minutes to build a stable droplet dispersion system. After emulsification, hold at this temperature for 15 minutes, then turn off the heating and turn on the jacket cooling water to begin primary cooling at a natural cooling rate.

[0035] Step 4: Phase locking and interpenetration process at critical temperature The material temperature was continuously monitored during the cooling process. When the system temperature dropped to 50℃, the pulse homogenization program was immediately started: homogenize at a frequency of 40Hz for 30 seconds, then pause for 1 minute, and repeat this cycle 3 times; while performing pulse homogenization, the jacket cooling water flow rate was increased to rapidly cool the system at a forced cooling rate of 3℃ / min.

[0036] Step 5: Add the active ingredients and degas under low pressure. Once the system has been cooled to 39°C by forced cooling, add 0.05 parts by weight of the pre-dissolved and mixed Stephania tetrandra extract, 0.05 parts by weight of the raspberry ketone glucoside solution, 0.3 parts by weight of the preservative, and 0.05 parts by weight of the flavoring. Start the wall-scraping agitator at 20 rpm and mix for 10 minutes. During this stage, perform vacuum degassing on the main pot, strictly controlling the vacuum level to -0.05 MPa.

[0037] Step 6: Inspection and Discharge After the system is further cooled to 30°C, the vacuum is released. After sampling and testing to ensure that the appearance, pH value, and rheological properties are qualified, the material is filtered through a 200-mesh filter to obtain the target high SPF transparent sunscreen gel.

[0038] Example 2: This example provides a high SPF transparent sunscreen gel and its preparation method. The composition, by weight, consists of the following components: Phase A: 63.0 parts by weight of deionized water, 2.0 parts by weight of phenylbenzimidazole sulfonic acid, 0.5 parts by weight of potassium hydroxide, 4.0 parts by weight of 1,3-butanediol, 4.0 parts by weight of glycerol, 0.8 parts by weight of sodium chloride, and 1.0 part by weight of vinylpyrrolidone / vinyl acetate copolymer aqueous solution (VP / VA copolymer 73W). Phase B: 3.5 parts by weight of ethylhexyl salicylate, 1.5 parts by weight of PEG-10 polydimethylsiloxane, 2.0 parts by weight of polydimethylsiloxane PEG-10 / 15 crosslinked polymer, 12.0 parts by weight of cyclopentadimethylsiloxane, and 5.0 parts by weight of the silicone elastomer prepolymer dispersion obtained in Preparation Example 2; Phase C: 0.1 parts by weight of Stephania tetrandra extract, 0.1 parts by weight of raspberry ketone glucoside, 0.4 parts by weight of preservative (phenoxyethanol and ethylhexylglycerin in conventional proportions), and 0.1 parts by weight of fragrance.

[0039] Its preparation method includes the following steps: Step 1: Preparation of Phase A Most of the deionized water and 2.0 parts by weight of phenylbenzimidazole sulfonic acid were added to an aqueous reaction vessel and stirred. 0.5 parts by weight of potassium hydroxide were dissolved in a small amount of reserved deionized water and then slowly added dropwise to the system under close monitoring. The pH of the system was precisely adjusted to 7.0 to ensure complete salt dissolution of the sunscreen agent and a clear, crystal-free system. Subsequently, 4.0 parts by weight of 1,3-butanediol, 4.0 parts by weight of glycerol, 0.8 parts by weight of sodium chloride, and 1.0 parts by weight of an aqueous solution of vinylpyrrolidone / vinyl acetate copolymer were added sequentially. The mixture was stirred at 350 rpm and heated to 85°C to form a homogeneous and transparent phase A solution, which was then kept at this temperature for later use.

[0040] Step 2: Preparation of Phase B 3.5 parts by weight of ethylhexyl salicylate, 1.5 parts by weight of PEG-10 polydimethylsiloxane, 2.0 parts by weight of polydimethylsiloxane PEG-10 / 15 crosspolymer, 12.0 parts by weight of cyclopentamethoxydimethylsiloxane, and 5.0 parts by weight of the silicone elastomer prepolymer dispersion synthesized in Preparation Example 2 were sequentially added to the main emulsifying vessel. A closed stirring valve was turned on, and the mixture was heated to 85°C and mixed at low speed until homogeneous. The mixture was then set aside.

[0041] Step 3: High-temperature initial emulsification Maintain the main pot temperature at 85℃, turn on the homogenizer, and set the homogenization frequency to 45Hz. Slowly and uniformly add phase A (85℃) to phase B under negative pressure. Maintain this temperature and homogenization conditions for 8 minutes to build a stable droplet dispersion system. After emulsification, hold at this temperature for 20 minutes, then turn off the heating and turn on the jacket cooling water to begin primary cooling at a natural cooling rate.

[0042] Step 4: Phase locking and interpenetration process at critical temperature The material temperature was continuously monitored during the cooling process. When the system temperature dropped to 55℃, the pulse homogenization program was immediately started: homogenize at a frequency of 45Hz for 45 seconds, then pause for 1.5 minutes, and repeat this cycle 4 times; while performing pulse homogenization, the jacket cooling water flow rate was increased to rapidly cool the system at a forced cooling rate of 4℃ / min.

[0043] Step 5: Add the active ingredients and degas under low pressure. Once the system has been cooled to 42°C by forced cooling, add 0.1 parts by weight of the pre-dissolved and mixed Stephania tetrandra extract, 0.1 parts by weight of the raspberry ketone glucoside solution, 0.4 parts by weight of the preservative, and 0.1 parts by weight of the flavoring. Start the wall-scraping agitator at 25 rpm and mix for 12 minutes. During this stage, perform vacuum degassing on the main pot, strictly controlling the vacuum level at -0.06 MPa.

[0044] Step 6: Inspection and Discharge After the system is further cooled to 32°C, the vacuum is released. After sampling and testing to ensure that the appearance, pH value, and rheological properties are qualified, the material is filtered through a 200-mesh filter to obtain the target high SPF transparent sunscreen gel.

[0045] Example 3: This example provides a high SPF transparent sunscreen gel and its preparation method. The composition, by weight, consists of the following components: Phase A: 50.85 parts by weight of deionized water, 3.0 parts by weight of phenylbenzimidazole sulfonic acid, 0.7 parts by weight of potassium hydroxide, 5.5 parts by weight of 1,3-butanediol, 5.5 parts by weight of glycerol, 1.0 part by weight of sodium chloride, and 1.5 parts by weight of vinylpyrrolidone / vinyl acetate copolymer aqueous solution (VP / VA copolymer 73W). Phase B: 5.0 parts by weight of ethylhexyl salicylate, 2.0 parts by weight of PEG-10 polydimethylsiloxane, 3.0 parts by weight of polydimethylsiloxane PEG-10 / 15 crosslinked polymer, 14.0 parts by weight of cyclopentadimethylsiloxane, and 7.0 parts by weight of the silicone elastomer prepolymer dispersion obtained in Preparation Example 3; Phase C: 0.15 parts by weight of Stephania tetrandra extract, 0.15 parts by weight of raspberry ketone glucoside, 0.5 parts by weight of preservative (phenoxyethanol and ethylhexylglycerin in conventional proportions), and 0.15 parts by weight of fragrance.

[0046] Its preparation method includes the following steps: Step 1: Preparation of Phase A Most of the deionized water and 3.0 parts by weight of phenylbenzimidazole sulfonic acid were added to an aqueous reaction vessel and stirred. 0.7 parts by weight of potassium hydroxide were dissolved in a small amount of reserved deionized water and then slowly added dropwise to the system under close monitoring. The pH of the system was precisely adjusted to 7.0 to ensure complete salt dissolution of the sunscreen agent and a clear, crystal-free system. Subsequently, 5.5 parts by weight of 1,3-butanediol, 5.5 parts by weight of glycerol, 1.0 part by weight of sodium chloride, and 1.5 parts by weight of an aqueous solution of vinylpyrrolidone / vinyl acetate copolymer were added sequentially. The mixture was stirred at 400 rpm and heated to 90°C to form a homogeneous and transparent phase A solution, which was then kept at this temperature for later use.

[0047] Step 2: Preparation of Phase B 5.0 parts by weight of ethylhexyl salicylate, 2.0 parts by weight of PEG-10 polydimethylsiloxane, 3.0 parts by weight of polydimethylsiloxane PEG-10 / 15 crosspolymer, 14.0 parts by weight of cyclopentamethoxydimethylsiloxane, and 7.0 parts by weight of the silicone elastomer prepolymer dispersion synthesized in Preparation Example 3 were sequentially added to the main emulsifying vessel. A closed stirring valve was turned on, and the mixture was heated to 90°C and mixed at low speed until homogeneous.

[0048] Step 3: High-temperature initial emulsification Maintain the main pot temperature at 90℃, turn on the homogenizer, and set the homogenization frequency to 50Hz. Slowly and uniformly add phase A (at 90℃) to phase B under negative pressure. Maintain this temperature and homogenization conditions for 10 minutes to build a stable droplet dispersion system. After emulsification, hold at this temperature for 30 minutes, then turn off the heating and turn on the jacket cooling water to begin primary cooling at a natural cooling rate.

[0049] Step 4: Phase locking and interpenetration process at critical temperature The material temperature was continuously monitored during the cooling process. When the system temperature dropped to 60℃, the pulse homogenization program was immediately started: homogenize at a frequency of 50Hz for 60 seconds, then pause for 2 minutes, and repeat this cycle 5 times; while performing pulse homogenization, the jacket cooling water flow rate was increased to rapidly cool the system at a forced cooling rate of 5℃ / min.

[0050] Step 5: Add the active ingredients and degas under low pressure. Once the system has been cooled to 45°C by forced cooling, add 0.15 parts by weight of the pre-dissolved and mixed Stephania tetrandra extract, 0.15 parts by weight of the raspberry ketone glucoside solution, 0.5 parts by weight of the preservative, and 0.15 parts by weight of the flavoring. Start the wall-scraping agitator at 30 rpm and mix for 15 minutes. During this stage, perform vacuum degassing on the main pot, strictly controlling the vacuum level at -0.08 MPa.

[0051] Step 6: Inspection and Discharge After the system is further cooled to 35°C, the vacuum is released. After sampling and testing to ensure that the appearance, pH value, and rheological properties are qualified, the material is filtered through a 200-mesh filter to obtain the target high SPF transparent sunscreen gel.

[0052] Comparative Examples 1-4: Comparative Example 1: Compared to Example 2, the difference is that the phase locking and interface interpenetration process at the critical temperature in step 4 is omitted. That is, after the high-temperature initial emulsification is completed, the system is directly cooled naturally in a conventional manner, accompanied by continuous low-speed stirring until it reaches the discharge temperature. Pulse homogenization at the critical temperature (55°C) is not performed, nor is jacketed forced rapid cooling (4°C / min). Everything else is the same.

[0053] Comparative Example 2: Compared to Example 2, the difference lies in that: in steps 1 and 3, the full amount of deionized water was not added to phase A for high-temperature initial emulsification; instead, 30 parts by mass of deionized water were reserved from the total formulation. This reserved deionized water was directly added to the system as a free aqueous phase in step 5 (i.e., the stage of adding the functional components when the system is cooled to 42°C) for mixing. The remaining components and process steps are the same.

[0054] Comparative Example 3: Compared to Example 2, the difference lies in that: in the preparation of phase A in step 1, 0.5 parts by mass of potassium hydroxide were omitted, and the salt formation neutralization operation and pH adjustment were not performed (at this time, the system is strongly acidic). The missing 0.5 parts by mass were made up with an equal amount of deionized water. The remaining components and process steps are the same.

[0055] Comparative Example 4: Compared to Example 2, the difference lies in that the critical temperature point for triggering the pulsed homogenization process and forced rapid cooling in step 4 is significantly shifted from 55°C to 75°C (prematurely triggering the high-temperature zone). All other aspects remain the same.

[0056] Test Examples 1-5: Test Example 1: Rheological Properties and 3D Network Anchoring Force Test This test aims to verify the structural strength of the three-dimensional cross-linked network within the formulation system. The experimental subjects are the sunscreen gel samples prepared in Examples 1, 2, and 3, as well as Comparative Examples 1 and 4. Comparative Example 2 was not included in this test because it had already undergone severe demulsification during the preparation stage, and Comparative Example 3 contained a large amount of undissolved solid crystals that would interfere with the gap setting of the rheological fixture.

[0057] The experimental samples were stored in a constant temperature room at 25°C for 48 hours to eliminate residual thermal stress and shear history.

[0058] The measurements were performed using a rotational rheometer equipped with a 40mm diameter parallel plate clamp. An appropriate amount of sample was transferred to the lower test stage of the rheometer, and the upper test plate was lowered to the set gap of 1.0mm. Excess sample from the edges was scraped off using a Teflon scraper.

[0059] The constant temperature water bath temperature of the test platform was set to 25℃. After the sample was loaded, it was allowed to stand and balance for 5 minutes to allow the material structure to return to a steady state between the fixtures.

[0060] Dynamic strain scanning tests were conducted with a fixed angular frequency of 10 rad / s and a strain range set from 0.01% to 100%, using logarithmic data acquisition mode. The average storage modulus of each sample in the linear viscoelastic region was recorded. .

[0061] Steady-state thixotropic ring tests were performed on the same batch of fresh samples at the same temperature. The shear rate was set from 0.1 s⁻¹. -1 linearly increased to 100s -1 Hold for 60 seconds, then for 100 seconds. -1 Linearly decrease to 0.1s -1 The closed area enclosed by the upward and downward curves is recorded, and the initial yield stress of the sample is calculated by fitting and extrapolating using the instrument's built-in software.

[0062] Table 1. Rheological property test results of the examples and comparative examples

[0063] Summarize: Figure 1 This is a dynamic strain scanning storage modulus curve of the embodiments and comparative examples of the present invention. The figure includes the test data points and trends of Embodiment 1, Embodiment 2, Embodiment 3, Comparative Example 1, and Comparative Example 4. All axes are logarithmic (X-axis: shear strain 0.01-100%, Y-axis: storage modulus). (100-3000 Pa). The data for the example group are marked with solid marks (squares, circles, triangles) and connected by solid lines, showing the decay profile of maintaining high modulus in the linear region and relatively hysteretic yielding in the high strain range; the comparative group is marked with hollow rhombuses and stars with dashed or dotted lines, highlighting its characteristic of structural collapse at lower shear strains.

[0064] Based on the data in Table 1, combined with Figure 1 The modulus decay trend of the curve under large strain in a double logarithmic coordinate system shows that the cooling process has a decisive influence on the network structure of high internal phase emulsions. In routine formulation development, storage modulus... The ability to directly map the continuous phase within a system to encapsulate the dispersed phase. Examples 1-3 The values ​​are all stable at a relatively high level above 1500 Pa, and the yield stress is distributed between 45-61 Pa. The rheological characteristics indicate that a dense physical entanglement has been formed between the silicone elastomer prepolymer and the silicone oil. Figure 1 In the intermediate embodiment, the nonlinear modulus cliff only begins to appear when the strain reaches the range of 15-22%. Conventional natural cooling cannot constrain the thermodynamic state of the water phase, which is over 70%. Comparative Example 1, by omitting the pulse and rapid cooling steps, The value dropped back to 642.1 Pa, and the thixotropic ring area shrank to about 1 / 3 of that in the previous embodiment. Figure 1 The results show that structural collapse occurred when the strain reached only around 5%. This phenomenon indicates that the dispersed fine water droplets merged under the influence of Brownian motion during the slow cooling process, and the silicon elastomer film that should have surrounded the droplets failed to solidify in time, resulting in a precipitous drop in the system's macroscopic resistance to deformation.

[0065] When studying the pulsed homogeneous triggering conditions, strict boundary restrictions were observed in the selection of the temperature window. In Comparative Example 4, the initial temperature for phase locking was set earlier to 75℃, and the measured yield stress was only 18.7 Pa. The critical strain in the dynamic scan also yielded early at around 8%. At higher temperatures, the overall viscosity of the continuous phase was relatively low, and the efficiency of high-frequency shearing in breaking up large droplets was acceptable. However, the kinetic energy of the polysiloxane segments was too high, making it difficult to form an effective three-dimensional interpenetrating residence in the droplet gaps. After the shear force was removed, the network structure that failed to reach the critical cross-linking state rapidly relaxed or even disintegrated under the action of internal osmotic pressure. This scheme couples the cooling rate with the 50-60℃ temperature point, utilizing the rheological abrupt change region where the system viscosity jumps sharply. Forced cooling and superimposed pulsed shearing during this window period can instantly freeze the emulsion interface. The high thixotropic ring area confirms that the gel formed by this locking process has a strong tendency to recombine the residual network fragments after being damaged by external force application, providing a physicochemical basis for the formation of a uniform and strongly adhesive film of sunscreen on the skin surface.

[0066] Test Example 2: Visible Light Transmittance Test (Quantitative Analysis of Optical Transparency) This test measures the transmittance in the visible light region to macroscopically evaluate the particle size control and refractive index matching of the dispersion medium in a high internal phase system. The experimental subjects used in this test were Examples 1, 2, and 3, as well as Comparative Examples 1 and 4. Comparative Example 2 was not included in this group of optical quantitative tests because macroscopic water-oil separation had already occurred, and Comparative Example 3 contained a large amount of undissolved solid crystals; both exhibited a severely opaque and turbid state, exceeding the effective measurement range of the instrument.

[0067] Samples were collected and stored at 25°C in the dark for 24 hours, then transferred to dedicated centrifuge tubes and centrifuged at a low speed of 1000 rpm for 3 minutes in a constant-temperature centrifuge. This operation aims to eliminate tiny air bubbles that may be trapped inside the feed during stirring and filling, thus eliminating additional light scattering interference caused by the bubble interface.

[0068] Select a standard quartz cuvette with a 10mm optical path length. Use a disposable plastic pipette to slowly pour the processed sample into the cuvette from the bottom, avoiding any air pockets. After filling, use a lint-free wiping paper to clean any oil or fingerprints from the outside of the cuvette.

[0069] Turn on the dual-beam UV-Vis spectrophotometer and warm it up for 30 minutes for baseline calibration, using a quartz cuvette of the same specification filled with deionized water as a blank reference optical path.

[0070] The scanning wavelength range was set to 400-800 nm in the measurement software, the data acquisition interval was set to 1 nm, and the scanning speed was set to medium. Full-band spectral scanning was performed on the cuvettes of each sample, and the light transmittance curves were measured.

[0071] Record and export full-spectrum data, and extract the exact light transmittance values ​​at three representative wavelength nodes: 450nm (blue light region), 600nm (yellow light region), and 750nm (red light region) for comparative analysis.

[0072] Table 2. Visible light transmittance data at different wavelengths for examples and comparative examples.

[0073] Summarize: Figure 2This is a visible light transmittance spectrum curve of the embodiments and comparative examples of the present invention. From top to bottom, the graph shows the transmittance variation trajectories of Embodiment 2, Embodiment 1, Embodiment 3, Comparative Example 4, and Comparative Example 1 in the 400-800nm ​​wavelength range. The graph uses a grayscale display design, and the arrangement of dense and sparse markers effectively avoids data overlap. Embodiment 2 is represented by a solid line with hollow dots, Embodiment 1 by a dashed line with solid triangles, and Embodiment 3 by a dotted line and hollow squares. These three sets of data curves are all densely distributed in the high transmittance region above 80%. Comparative Example 4 and Comparative Example 1 are represented by a dotted line with a solid rhombus and a thin solid line with an asterisk, respectively. Their transmittance curves not only show a significant downward position overall but also exhibit nonlinear fluctuation characteristics that closely resemble the actual testing environment.

[0074] Based on the data distribution shown in Table 2, the optical transparency of the system exhibits significant differences after undergoing different cooling and shearing processes. In routine laboratory studies of high-internal-phase sunscreen gel formulations, it was observed that optical transparency requires not only a high degree of refractive index matching between the continuous and dispersed phases but also ensuring that the internal droplet diameter is much smaller than the visible light wavelength limit. Even with the addition of butanediol and glycerol to the aqueous phase to reduce the refractive index difference with the external silicone oil, the material, lacking effective thermodynamic intervention, is still prone to whitening due to spontaneous droplet aggregation. The example sample maintained a transmittance of over 85% across the entire visible light region, demonstrating that the forced rapid cooling and pulsed homogenization mechanism successfully froze the microstructure of the emulsion interface. The interface was firmly anchored by the silicone elastomer network before the droplets had time to undergo Australtic ripening and merging. The size of the dispersed phase droplets was limited below the critical threshold for Mie scattering, resulting in extremely low refractive loss when light penetrates the medium, and a macroscopically uniform and clear state.

[0075] Observing the light transmission behavior of the comparative examples can inversely verify the sensitivity of the thermodynamic steady state of the interface. Comparative Example 1, lacking a pulse-locking mechanism, allowed sufficient time for the aqueous droplets to break free from the interfacial tension during the slow cooling phase, resulting in a sharp drop in transmittance to 40.54% at 600 nm. The spontaneous aggregation of droplets into larger droplets of several micrometers or even tens of micrometers directly amplified the optical path difference between the different phase interfaces, and severe light scattering caused the system to exhibit a completely opaque, milky-white state. Prematurely triggering the cooling and solidification process also failed to maintain the long-term stability of the microstructure. Comparative Example 4 intervened early at 75°C, and although the transmittance slightly increased to 53.27% compared to Comparative Example 1, the elastomer prepolymer was still in a stretched and active state at higher temperatures, failing to establish an effective network framework to encapsulate the water droplets. After the external force was removed, the droplets continued to expand slowly internally; this structural decay of the microstructure was easily captured by the collapse of light transmittance. A significant decrease in light transmittance is usually an early sign that the physical structure of the emulsion is becoming completely unstable. This directly explains the underlying reason why the comparative formula with cooling process defects is unable to maintain the uniformity of sunscreen ingredient distribution during subsequent resting or application.

[0076] Test Example 3: Comparative Test of Extreme Thermodynamic Stability (Evaluation of Demulsibility and Water Separation Resistance) This test examines the physical anchoring limit of a high internal phase emulsion network structure under harsh conditions by introducing a strong centrifugal force field and a drastic alternation of high and low temperatures. The subjects included in this evaluation group are Examples 1, 2, and 3, as well as Comparative Examples 1 to 4, which have process or formulation defects.

[0077] Take 15 grams of the material from each batch after it has been prepared and left to stand for 24 hours, weigh it precisely, and fill it into a special centrifuge tube with a 0.1 mL precision scale. Seal the tube opening to prevent moisture evaporation.

[0078] Place the filled centrifuge tubes symmetrically inside the rotor of a large-capacity benchtop centrifuge. Set the operating environment to room temperature, increase the centrifugation speed to 4500 rpm, and run for 40 minutes. After the centrifugation program is complete, remove the sample and observe whether a clear or turbid aqueous free layer appears at the bottom of the tube. Read the scale and calculate the centrifugation water yield.

[0079] Samples from the same batch were placed in transparent wide-mouth glass bottles and sealed. The bottles were then placed in a programmable high and low temperature test chamber for environmental stress screening. The single-cycle curve was set to maintain a high temperature of 45℃ for 12 hours, followed by cooling to -15℃ and maintaining the temperature for 12 hours. This process was repeated for 3 complete cycles.

[0080] After the freeze-thaw cycle was terminated, the glass bottles were transferred to a 25°C room temperature test bench for natural thawing for 24 hours. The macroscopic physical state of the material was recorded at this time. The samples were then placed into graduated tubes using the same sampling method and centrifuged for 20 minutes at 3000 r / min to verify the residual structural strength of the material after thermal stress fatigue.

[0081] Table 3. Quantitative stability assessment data of the examples and comparative examples under different harsh conditions.

[0082] Summarize: Figure 3 This is a graph showing the distribution of forced water separation rate under centrifugal stress in the embodiments and comparative examples of this invention. The horizontal axis represents Examples 1-3 and Comparative Examples 1-4, respectively, while the vertical axis shows the centrifugal water separation rate ranging from -2% to 40%. Solid black circles and solid lines depict the water separation rate distribution during the initial high-speed centrifugation stage at room temperature; hollow squares and dashed lines depict the secondary water separation rate decay trend after high-low temperature freeze-thaw cycles. Vertical black dotted lines connect the two water separation rate data points of the same test object, visually highlighting the structural decay amplitude before and after forced thermal stress intervention.

[0083] According to Table 3 and Figure 3 The data distribution characteristics show that the strong centrifugal force field exerted extreme physical pressure on the high internal phase emulsion system, forcing the heavier internal phase water droplets to overcome interfacial tension and migrate towards the bottom of the test tube. When evaluating the weather resistance of conventional high internal phase gels, the laboratory often faces the technical challenge of centrifugal phase separation. Comparative Examples 1 and 4 showed initial water separation rates of 5.87% and 3.61% respectively during room temperature centrifugation. After thermal stress cycling, the secondary breakage and water separation rates of both soared to 13.42% and 8.95%. Figure 3 The relatively long spans of these two sets of vertical connecting lines reflect the existence of significant physical structural voids within the silicone elastomer network, which failed to be precisely locked by the cooling rate. Insufficient interpenetration depth of molecular chain segments prevents the cross-linked network from effectively covering the surrounding water droplets when subjected to external mechanical energy or thermal expansion and contraction stress. In contrast, the example group exhibited stable performance. Even under the intense volume expansion and contraction effects caused by alternating high temperatures of 45°C and freezing at -15°C, the deformation of the three-dimensional network within the example remained within the elastic range. The interfacial film exhibited extremely high density and flexibility, with moisture firmly locked in the center of the grid. The water separation rate remained within the limits of instrumental observation error, and no macroscopic turbidity or stratification was observed.

[0084] The deliberately introduced formulation defects in the comparative studies further revealed the stringent conditions required for the micro-network to maintain thermodynamic equilibrium. The direct addition of unhomogenized free water in the later stages of formulation is often a major hidden danger in industrial-scale production. The instantaneous osmotic pressure imbalance in Comparative Example 2 triggered an irreversible chain reaction. A large amount of uncoated free water directly washed away the already nascent three-dimensional silica-based network, resulting in a water separation rate as high as 29.53% at room temperature, and complete disintegration into free water and oil layers after freeze-thaw cycles. The incompletely neutralized phenylbenzimidazole sulfonic acid solid crystals were another serious, hidden source of damage. In Comparative Example 3, the dispersed hard crystal particles, driven by high-speed centrifugal force, became micro-abrasive media, inevitably piercing the thin silica interface film encapsulating water droplets, forming numerous micro-demulsification centers. With the rapid spread of these physically damaged interfaces, the transparent and stable state established by the synergistic effect of electrolytes and the interface film was completely shattered, resulting in a secondary water separation rate of 26.54%. Microscopic particle puncture directly caused extreme thinning and stratification of the macroscopic material texture, confirming that the compatibility and uniformity within the sunscreen system have a decisive influence on the overall anti-demulsification limit.

[0085] Test Example 4: Quantitative Evaluation of In Vitro SPF Sun Protection Efficacy and Film Formation Uniformity This group of tests was used to verify the actual impact of the integrity of the microstructure of the highly transparent internal phase system on the macroscopic sun protection efficacy and coating uniformity after undergoing thermodynamic interventions at different interfaces. The experimental subjects involved in the in vitro determination included Examples 1, 2, and 3, where the formulation and process parameters were controlled within the set range, as well as Comparative Examples 1, 2, 3, and 4, which had control interventions.

[0086] A PMMA (polymethyl methacrylate) quartz biomimetic test plate with a surface roughness of 5μm was selected as the substrate. Before the test, the surface was wiped clean with isopropanol and allowed to stand to evaporate until completely dry.

[0087] Each substrate was calibrated using a precision analytical balance, with a tare weight of 2.00 mg / cm³. 2 The internationally accepted sunscreen testing standard was used to apply the coating amount of each group of experimental samples to the substrate surface using a syringe.

[0088] The experimenters wore latex gloves and spread the dotted sample evenly with a constant pressing pressure and circular motion until the material formed a uniform film on the PMMA plate. The entire coating process was completed within 60 seconds.

[0089] The coated test plate was transferred to a light-proof constant temperature and humidity chamber at 25°C and 50% relative humidity, and allowed to stand for 20 minutes to allow the volatile components inside the film to reach equilibrium.

[0090] Turn on the in vitro ultraviolet transmittance analyzer and perform blank reference plate calibration. Place the PMMA plate after film formation in the sample cell, and randomly select 9 non-overlapping detection sites for full-band ultraviolet (290-400nm) transmittance scanning on each test plate.

[0091] The instrument's backend software extrapolates the average in vitro SPF value based on the absorbance at each wavelength, and simultaneously exports the standard deviation of SPF data from 9 detection sites, calculates the coefficient of variation (CV%), and uses it as a quantitative indicator of coating uniformity.

[0092] Table 4. In vitro SPF determination and film-forming coefficient of variation results for examples and comparative examples

[0093] Summarize: Figure 4 This is a biaxial trend chart of the in vitro sun protection index and film-forming coefficient of variation for the embodiments and comparative examples of this invention. The left primary axis is associated with a solid black line and a white hollow circle marker, corresponding to the fluctuation of the average in vitro SPF value of each sample; the right secondary axis is associated with a dashed black line and a solid black square marker, corresponding to the coefficient of variation of data distribution at multiple points on the same test plate. The axis scales are all set in the range of 0-80, involving Examples 1-3 and Comparative Examples 1-4, visually demonstrating the negative correlation between the absolute value of protective power and the uniformity of the film layer.

[0094] According to the data in Table 4, multi-point scanning of the coated PMMA plate confirmed that the SPF is not entirely dependent on the absolute concentration of sunscreen agent in the formulation; the rheological response of the carrier structure largely dominates the final optical protection performance. In laboratory evaluations of the film-forming properties of high internal phase systems, it is often found that the yield state of the cross-linked network within the system directly determines the spreadability of the material. When the sample in the examples was subjected to fingertip pressure shearing, the silicon-based three-dimensional network locked by the temperature window and rapid cooling process underwent smooth deconstruction. This uniform thixotropic recovery characteristic allows the water-soluble sunscreen components encapsulated in the internal phase to be smoothly distributed on the substrate surface along with the polysiloxane segments. Examples 1-3 not only obtained SPF values ​​consistent with the formulation design, but their coefficient of variation was also suppressed to a low level of less than 7%, indicating that the sunscreen film exhibits a dense, unbroken state at the microscale, effectively avoiding the risk of ultraviolet light penetrating through weak areas.

[0095] Observing the comparative examples with defects in process and formulation intervention, the loss of sun protection power caused by the discontinuity of the coating film was particularly obvious. Comparative Example 3 omitted the alkali neutralization operation, and the large number of free phenylbenzimidazole sulfonic acid crystal particles in the aqueous phase blocked the rheological extensibility of the system, resulting in severe local agglomeration of particles during the coating process. Light directly penetrated through the gaps between particles that lacked effective UV absorber coverage, causing the coefficient of variation to soar to 61.32%, and the average SPF value to plummet to only 21.05. In Comparative Examples 1 and 4, due to the failure to accurately control the critical point of the interpenetration and anchoring of the cooling network, the material exhibited obvious water separation and stagnation when subjected to physical coating shear. The forced separation of the inner and outer phases destroyed the original uniform dispersion of the sunscreen, and the fusion of local droplets caused uneven coating thickness. Under the premise of the same amount of sunscreen added, the average SPF value showed a 20-30% performance loss compared to the examples. This phenomenon reveals that when formulating high internal phase sunscreen systems, the demulsification or cross-linking network relaxation caused by the intervention of free water is the underlying physicochemical cause that weakens the continuity of film formation and ultimately leads to the failure of end-point protection performance.

[0096] Test Example 5: Blind Testing and Rating of Consumer Sensory Experience and Skin Feel This test establishes a standardized sensory evaluation model to transform the physical state of the formulation's microscopic interface into intuitive tactile and visual quantitative data for end users. The experimental subjects participating in this sensory evaluation were Examples 1, 2, and 3, as well as Comparative Examples 1, 2, 3, and 4.

[0097] Thirty-five healthy adult volunteers with basic sensory evaluation training were recruited. Participants were required to have no history of topical medication use and no skin breakage on the inside of their arms within one week prior to testing. All tests were conducted in a standardized temperature and humidity controlled assessment laboratory at 24±1℃ and 45±5% relative humidity.

[0098] After the samples were allowed to stand and stabilize, they were packaged into uniform white light-proof vacuum pump bottles. Only a randomly generated four-digit blind code was marked on the outside of the bottle to shield the evaluation results from the interference of subjective brand or formula pre-set bias.

[0099] Before the test began, volunteers cleaned and dried the inside of both forearms with a neutral cleansing solution and sat quietly for 15 minutes to acclimatize. The experimenter then used a pipette to accurately measure 0.10 mL of sample and applied it to a 5×5 cm grid area marked on the inside of the volunteer's forearm.

[0100] Volunteers applied the coating five times consecutively in the same direction using the pads of their index and middle fingers with moderate pressure, following the prescribed guidelines. During and immediately after application, scores were given based on three core dimensions: the smoothness of the coating (assessing the smoothness of spread after contact with body temperature and shear force), visual transparency (assessing the clarity of the coated film and the absence of whitening), and the roughness of the coating (assessing the presence of microparticles or a gritty feel). The scores were converted to a quantitative value of 1-10 using a continuous linear scaling method.

[0101] For the first two indicators, a higher score indicates smoother water spread and greater visual transparency; for the roughness of the sand, a higher score indicates a stronger sense of graininess and friction. After evaluating each sample, volunteers were required to wash the test area with warm water and wait at least 2 hours before proceeding to the next blind test. All valid rating sheets were collected, and the arithmetic mean was calculated after removing extreme values.

[0102] Table 5. Consumer sensory and skin feel blind test scores for the examples and comparative examples.

[0103] Summarize: Figure 5 This is a multi-line comparison chart of the three-dimensional sensory evaluation dimensions of the embodiments and comparative examples of the present invention. The horizontal axis represents the test objects of different embodiments and comparative examples, and the vertical axis represents the blind test scores of sensory evaluation ranging from 0 to 10. To intuitively present the differences in the distribution of multi-dimensional data, three different grayscale line types and marker symbols are used in the chart. Specifically, the data trajectory reflecting the spreadability of the smeared material is connected by a solid black line and a solid black circle; the data reflecting visual clarity and lack of whiteness is represented by a dashed black line with a hollow white triangle; and the numerical changes in the roughness of the gritty texture are depicted using a dotted line and a solid gray square. This differentiation of multiple visual features avoids the interference of overlapping dense data points and clearly shows the changing trends of various core tactile and visual indicators between embodiments 1-3 and comparative examples 1-4.

[0104] Based on the data in Table 5, combined with Figure 5The score distribution across various dimensions reveals a direct mapping between the macroscopic skin feel feedback and the integrity of the internal three-dimensional cross-linked network of the high internal phase sunscreen system. During the establishment of the human evaluation model in the laboratory, it was observed that the "water-like" sensation is not simply a tactile deviation caused by rapid water evaporation, but rather a macroscopic manifestation of the thixotropic yielding of the gel's internal network structure under the shear force of fingertip pressure. The example group generally scored over 8 points in the "water-like" spreadability dimension, thanks to the critical quenching process precisely locking the optimal microstructure of the water droplets encapsulated in the silicone elastomer. When the system is applied through physical friction, the dense and elastic interfacial film rapidly undergoes structural deconstruction, instantly releasing a large amount of aqueous alcohol solvent encapsulated in the internal phase, achieving smooth spread on the skin surface. The thermodynamic stability of this microscopic phase also ensures the visual clarity of the material during application and after film formation, resulting in the example group leading in all positive indicators among all tested samples.

[0105] Formulation systems devoid of precise thermodynamic intervention often exhibit significant degradation in sensory performance. Uncontrolled natural cooling or misaligned temperature windows directly led to a decline in skin feel evaluation; Comparative Examples 1 and 4 showed significantly reduced water-like feel scores and revealed visual whitening defects in blind testing. The lack of instantaneous forced anchoring conditions made the continuous silicone oil phase prone to irregular micro-fractures under shear stress, causing premature coalescence of aqueous droplets during frictional heating. Strong diffuse reflection occurred when light passed through the mixed medium of varying sizes and chaotic phase interfaces, resulting in white marks and a heavy feel in the end-user's visual perception. We observed the destructive effect of chemical imbalance on tactile sensation when extreme formulation conditions were introduced. Comparative Example 3 omitted the acid-base neutralization step; free phenylbenzimidazole sulfonic acid caused the material to appear as a turbid mud-like substance. Undissolved rigid crystalline particles formed a micro-abrasive medium on the skin surface, causing the gritty roughness index to soar to an extreme value of 9.47. This confirms that any substance in the formula that is not properly solubilized or lacks a stable three-dimensional cross-linked network will weaken the formula's texture by reducing interfacial compatibility, suggesting that maintaining the stability of the microstructure is an irreplaceable role in the development of sunscreen systems.

Claims

1. A high SPF transparent sunscreen gel, characterized in that, The transparent sunscreen gel, by weight, comprises the following components: Phase A components used in aqueous base and water-soluble sunscreen phase: 50.85-75.25 parts deionized water; 1.0-3.0 parts phenylbenzimidazole sulfonic acid for water-soluble sunscreen agent; 0.3-0.7 parts potassium hydroxide for salting agent; 2.5-5.5 parts 1,3-butanediol and 2.5-5.5 parts glycerol for moisturizing agent; 0.5-1.0 parts sodium chloride for stabilizer; and 0.5-1.5 parts aqueous solution of vinylpyrrolidone / vinyl acetate copolymer for aqueous film-forming agent. Phase B components used in oil-based and oil-soluble sunscreen phases: 2.0-5.0 parts of ethylhexyl salicylate for oil-soluble sunscreen agents, 1.0-2.0 parts of PEG-10 polydimethylsiloxane and 1.0-3.0 parts of polydimethylsiloxane PEG-10 / 15 crosspolymer for emulsifiers, 10.0-14.0 parts of cyclopentamethoxysiloxane for solvents, and 3.0-7.0 parts of silicone elastomer prepolymer dispersion for rheology modifiers; C-phase components used for efficacy and modification: 0.05-0.15 parts of Stephania tetrandra extract, 0.05-0.15 parts of raspberry ketone glucoside, 0.3-0.5 parts of preservative, and 0.05-0.15 parts of fragrance.

2. The high SPF transparent sunscreen gel according to claim 1, characterized in that, The silicone elastomer prepolymer dispersion was obtained by the following preparation method: Under a protective atmosphere, 65.0-75.0 parts by weight of cyclopentamethoxysiloxane, 20.0-30.0 parts by weight of vinyl-terminated polydimethylsiloxane with a weight average molecular weight of 10,000-15,000 are used as the matrix resin and 3.0-6.0 parts by weight of hydrogen-containing polydimethylsiloxane are used as the crosslinking agent and mixed evenly. After heating to 60-65℃, slowly add isopropanol chloroplatinate solution as a catalyst to carry out hydrosilylation polymerization. Control the system temperature to maintain 75-80℃ and react for 2-3 hours. The sample was prepared by cooling after all free Si-H bonds had reacted completely. The amount of the isopropanol chloroplatinic acid solution used is 5-15 ppm of the total mass of the matrix resin and crosslinking agent.

3. A method for preparing a high SPF transparent sunscreen gel, characterized in that, The high SPF transparent sunscreen gel described in any one of claims 1-2 comprises the following preparation process: Deionized water and phenylbenzimidazole sulfonic acid were mixed and stirred. Deionized water containing dissolved potassium hydroxide was added to adjust the pH of the system to neutral. Then, 1,3-butanediol, glycerol, sodium chloride and vinylpyrrolidone / vinyl acetate copolymer aqueous solution were added in sequence, stirred and heated to obtain a homogeneous and transparent A phase component solution, which was kept warm for later use. Ethylhexyl salicylate, PEG-10 polydimethylsiloxane, polydimethylsiloxane PEG-10 / 15 cross-linked polymer, cyclopentadimethylsiloxane and silicone elastomer prepolymer dispersion were sequentially added to the main emulsifying pot, the sealed stirring was turned on and the temperature was raised, and the mixture was mixed at low speed to obtain phase B component for later use. Maintain the temperature of the main pot, turn on the homogenizer, and slowly and uniformly add the solution of phase A, which is at the same temperature as phase B, to phase B under negative pressure to maintain homogenization conditions; after emulsification, keep it warm, then turn off the heating and start primary cooling by natural cooling rate. During the cooling process, the material temperature is continuously monitored. When the system temperature drops to the critical phase lock-in temperature, that is, the temperature at which the polymer network of the system undergoes solidification transformation, the pulse homogenization program is immediately started. While performing pulse homogenization, forced cooling water is turned on to rapidly cool the system at the set forced cooling rate. Once the system has been cooled to the temperature required for adding the active ingredients using forced cooling, add the pre-dissolved and mixed Stephania tetrandra extract and raspberry ketone glucoside solution, preservatives, and fragrances in sequence; start the wall-scraping agitator to mix; and simultaneously perform vacuum degassing treatment on the main pot. After the system is further cooled to the discharge temperature, the vacuum is released, and the material is discharged after filtration to obtain the target high SPF transparent sunscreen gel.

4. The preparation method according to claim 3, characterized in that, The temperature for stirring and heating, and the temperature for opening the sealed stirring and heating are both 80-90℃. The pH of the system is adjusted to be neutral, specifically to a pH of 6.0-8.

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5. The preparation method according to claim 3, characterized in that, The stirring and heating process yields a homogeneous and transparent A-phase component solution, with the stirring speed set to 300-400 r / min.

6. The preparation method according to claim 3, characterized in that, The homogenizer is turned on, and the homogenization frequency of the homogenizer is set to 40-50Hz, and the homogenization conditions are maintained for 5-10 minutes. After emulsification, the mixture is kept warm for 15-30 minutes.

7. The preparation method according to claim 3, characterized in that, The critical phase lock-in temperature is 50-60℃ when the system temperature drops to the critical phase lock-in temperature. The pulse homogenization program operates by homogenizing at a frequency of 40-50Hz for 30-60 seconds, then pausing for 1-2 minutes, and repeating this cycle 3-5 times.

8. The preparation method according to claim 3, characterized in that, The forced cooling water is activated to rapidly cool the system at a set forced cooling rate of 3-5℃ / min.

9. The preparation method according to claim 3, characterized in that, When the system is subjected to forced cooling to the temperature at which the active ingredient is added, the temperature at which the active ingredient is added is 39-45℃. In the process of vacuum degassing the main pot, the vacuum degree of the vacuum degassing process is controlled within the range of -0.08 to -0.05 MPa.

10. The preparation method according to claim 3, characterized in that, During the mixing process, the wall-scraping agitator is set to a speed of 20-30 r / min and a mixing time of 10-15 min. The discharge temperature is 30-35℃.

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