A raspberry-shaped sunscreen nano-capsule, its preparation method and application

Abstract

The present invention relates to a raspberry-shaped sunscreen nano-capsule and its preparation method and application, belonging to the technical field of nano-capsules. The raspberry-shaped sunscreen nano-capsule of the present invention comprises a random amphiphilic copolymer solution, a sunscreen agent, an oil-phase monomer and an initiator; the concentration of the random amphiphilic copolymer solution is 8 g / L - 12 g / L; the mass ratio of the sunscreen agent to the oil-phase monomer is 1:1.8 - 2.2; the mass ratio of the random amphiphilic copolymer in the random amphiphilic copolymer solution to the oil-phase monomer is 0.5 - 1.25:1; the raspberry-shaped sunscreen nano-capsule has a self-assembled aggregate of the random amphiphilic copolymer as the outer shell layer and a polymer microsphere formed by polymerization of the oil-phase monomer as the core; the sunscreen agent is encapsulated in both the outer shell layer and the core; the surface of the raspberry-shaped sunscreen nano-capsule presents a raspberry-shaped structure. Combining the absorption effect of the sunscreen agent on ultraviolet light and the scattering and reflection effects of the nano-particles on the sunscreen agent, a full-band and highly efficient ultraviolet protection effect of the sunscreen nano-capsule is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of nano-capsules, and particularly relates to a raspberry-shaped sunscreen nano-capsule, a preparation method thereof and an application thereof. Background Art

[0002] After being absorbed and filtered by the ozone layer, the ultraviolet rays (UV) reaching the ground layer are composed of approximately 90% UVA and 10% UVB. When the human body is exposed to sunlight for a long time, in addition to causing sunburn, skin pigmentation, and wrinkles on the human skin, UVB and UVA will also directly or indirectly damage DNA, inducing diseases such as skin cancer and non-malignant melanoma. One of the most effective means of protecting against UV today is to apply sunscreen. However, current organic ultraviolet absorbers generally have photosensitivity and phototoxicity. In addition, to obtain a cream with high-efficiency ultraviolet protection, a large amount of organic sunscreen is usually required. Correspondingly, more oil-phase solvents also need to be compounded, resulting in an unpleasant experience such as greasiness and difficulty in spreading. With the improvement of people's living standards, people also pay more and more attention to the safety of sunscreen use and the skin feel experience.

[0003] Using encapsulation technology and means can avoid the contact between the sunscreen and the human body, effectively reducing the safety risk of use. At the same time, the encapsulated sunscreen will not precipitate from the oil-phase solvent, providing the possibility for preparing a high-SPF and non-greasy sunscreen formulation. However, existing encapsulation means for sunscreens have problems such as low encapsulation efficiency, high leakage rate, and inability to obtain an efficient ultraviolet protection effect. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a raspberry-shaped sunscreen nano-capsule, a preparation method thereof and an application thereof. The present invention combines miniemulsion polymerization and self-assembly of amphiphilic polymers to synthesize a raspberry-shaped sunscreen nano-capsule with a polymer microsphere formed by monomer polymerization as the core and a self-assembly body of a random amphiphilic copolymer as the outer shell layer. Both the core and the outer shell layer participate in the encapsulation of the sunscreen, with the outer shell layer playing a dominant role. This surface encapsulation technology and raspberry structure are both beneficial to improving the sunscreen performance. When encapsulating different types of sunscreens, ultraviolet full-band protection can be achieved.

[0005] The first object of the present invention is to provide a raspberry-shaped sunscreen nano-capsule, comprising a random amphiphilic copolymer solution, a sunscreen, an oil-phase monomer and an initiator; the concentration of the random amphiphilic copolymer solution is 8 g / L - 12 g / L; the mass ratio of the sunscreen to the oil-phase monomer is 1:1.8 - 2.2; the content of the initiator is 1% - 5% of the molar amount of the oil-phase monomer; the mass ratio of the random amphiphilic copolymer in the random amphiphilic copolymer solution to the oil-phase monomer is 0.5 - 1.25:1;

[0006] Among them, the raspberry-shaped sunscreen nano-capsules have a self-assembled aggregate of a random amphiphilic copolymer as the outer shell layer and a polymer microsphere formed by the polymerization of an oil-phase monomer as the core; sunscreen agents are encapsulated in both the outer shell layer and the core;

[0007] The surface of the raspberry-shaped sunscreen nano-capsules presents a raspberry-shaped structure.

[0008] In an embodiment of the present invention, through the encapsulation means, both the ultraviolet protection efficiency and the photo-stability of the sunscreen agent are improved. The improvement of the ultraviolet protection efficiency is due to the fact that the particles scatter and reflect part of the ultraviolet light, and the ultraviolet light that changes the optical path undergoes multiple reflections and refractions among the particles, which further increases the absorption efficiency of the sunscreen agent inside the nano-capsules for ultraviolet light, thereby reducing the amount of ultraviolet radiation passing through the sunscreen layer. The raspberry-shaped nano-capsules have sub-micron-sized dimensions and a relatively high surface roughness, which is more conducive to scattering and reflecting ultraviolet rays. On the other hand, compared with internal encapsulation, the sunscreen agent encapsulated in the surface layer is more conducive to improving the ultraviolet absorption efficiency of the sunscreen agent.

[0009] In an embodiment of the present invention, the random amphiphilic copolymer P(St-co-MAA) is copolymerized by mixing styrene and methacrylic acid in a molar ratio of 2:8 - 8:2 and through solution radical polymerization under the action of azobisisobutyronitrile (AIBN).

[0010] In an embodiment of the present invention, the application of the random amphiphilic copolymer has three functions: (1) a more excellent fine emulsion monomer droplet stabilizing effect: traditional small molecule emulsifiers generally stabilize the emulsion through adsorption at the oil-water interface, while amphiphilic polymer-based macromolecular emulsifiers also have hydrophilic segments and hydrophobic segments. When forming an emulsion, their hydrophobic segments are embedded inside the oil-phase droplets, and the hydrophilic segments stretch in the dispersed water phase. This different binding method enables the random amphiphilic polymer to better stabilize the original fine emulsion droplets. (2) Among macromolecular emulsifiers, compared with block copolymers and graft copolymers, random copolymers have the advantages of simple synthesis, low cost, and a wide selection of monomers. (3) Combining with the encapsulation efficiency experiment, the self-assembled layer of the amphiphilic polymer can participate in the encapsulation of the sunscreen agent, thereby significantly improving the encapsulation efficiency of the nano-capsules.

[0011] In an embodiment of the present invention, the sunscreen agent is obtained by mixing octyl dimethyl PABA (OD-PABA) and diethylamino hydroxybenzoyl hexyl benzoate (DHHB) in a mass ratio of 1:1 - 3.

[0012] In one embodiment of the present invention, there are two reasons for using a compound sunscreen: (1) DHHB belongs to a UVA sunscreen and OD-PABA belongs to a UVB sunscreen. By compound encapsulation of two different types of sunscreens, spectral protection against ultraviolet rays can be imparted to the nanocapsules. (2) If only DHHB is encapsulated, due to the limited solubility of the oil-phase monomer in DHHB, more oil-phase monomers need to be added. As a result, the loading rate of the nanocapsules prepared for the sunscreen is low. When adding the same mass of sunscreen nanocapsules (10 wt%), the prepared sunscreen may not achieve a high sun protection factor. However, the liquid oil-phase sunscreen OD-PABA can solubilize DHHB, reduce the addition of the oil phase, and increase the loading rate of the sunscreen.

[0013] In one embodiment of the present invention, the oil-phase monomer is obtained by mixing methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGAMA) in a molar ratio of 1:1 - 5.

[0014] In one embodiment of the present invention, the reason for using a compound oil-phase monomer is that: although the self-assembled layer of P(St-co-MAA) dominates the encapsulation of the sunscreen, the P(MMA-EGDMA) polymer particles also participate in the encapsulation of the sunscreen. The structure formed by the polymerization of MMA is a chain structure, and EGDMA acts as a cross-linking agent, and its polymerization forms a three-dimensional network structure, which is more conducive to the encapsulation of the sunscreen by the nanocapsules.

[0015] In one embodiment of the present invention, the initiator is azobisisobutyronitrile (AIBN).

[0016] In one embodiment of the present invention, the solvent of the random amphiphilic copolymer solution is a sodium hydroxide solution.

[0017] In one embodiment of the present invention, the concentration of the sodium hydroxide solution is 0.05 mol / L - 0.2 mol / L.

[0018] The second object of the present invention is to provide a method for preparing the raspberry-shaped sunscreen nanocapsules as described above, including the following steps.

[0019] (1) Dissolve the random amphiphilic copolymer in a sodium hydroxide solution to obtain a random amphiphilic copolymer solution (aqueous phase);

[0020] (2) Mix the sunscreen, the oil-phase monomer, and the initiator evenly to obtain an oil phase;

[0021] (3) Add the random amphiphilic copolymer solution described in step (1) to the oil phase described in step (2), and through pre-emulsification and fine emulsification, obtain an oil-in-water type fine emulsion;

[0022] (4) Under a nitrogen atmosphere, the oil-in-water type miniemulsion described in step (3) undergoes a polymerization reaction, and after washing and centrifugation, the raspberry-shaped sunscreen nano-capsules are obtained.

[0023] In one embodiment of the present invention, in step (4), the temperature of the polymerization reaction is 60°C - 70°C, and the time is 12 h - 24 h.

[0024] In one embodiment of the present invention, in step (4), the detergent used for washing is petroleum ether.

[0025] In one embodiment of the present invention, there are two advantages in choosing oil-in-water type miniemulsion polymerization: (1) The nucleation mechanism of traditional emulsion polymerization includes droplet nucleation and micelle nucleation, and the polymerization monomers migrate to the swollen micelles or the oligomeric hydrophobic chains formed by the monomers. The miniemulsion polymerization is characterized by droplet nucleation and in-situ polymerization, and the polymerization mainly occurs inside the miniemulsion monomer droplets, so the hydrophobic sunscreen dissolved in the oil-phase monomers can be efficiently encapsulated. (2) The miniemulsion monomer droplets are in the range of 50 - 500 nm, and this sub-micron size is comparable to the ultraviolet wavelength (200 - 400 nm), so the scattering and reflection effects on ultraviolet light are better.

[0026] The third object of the present invention is to provide a sunscreen, which is prepared from the raspberry-shaped sunscreen nano-capsules described above.

[0027] In one embodiment of the present invention, the concentration of the raspberry-shaped sunscreen nano-capsules in the sunscreen is 8 wt% - 10 wt%.

[0028] In one embodiment of the present invention, the sunscreen achieves high-efficiency ultraviolet protection through the absorption of the sunscreen and the scattering and reflection of the nanoparticles.

[0029] The technical solution of the present invention has the following advantages compared with the prior art:

[0030] (1) The raspberry-shaped sunscreen nano-capsules of the present invention use the random amphiphilic copolymer P(St-co-MAA) as the emulsifier for miniemulsification, and by stabilizing the monomer droplets in the miniemulsion, they are used to prepare nano-capsules encapsulating sunscreen.

[0031] (2) The raspberry-shaped sunscreen nano-capsules of the present invention combine miniemulsion polymerization with the self-assembly of the random amphiphilic copolymer P(St-co-MAA), and the formed core and shell jointly participate in the encapsulation of the sunscreen, and sunscreen nano-capsules with high encapsulation efficiency and low leakage rate are prepared.

[0032] (3) The self-assembly of the random amphiphilic copolymer P(St-co-MAA) on the surface of the raspberry-shaped sunscreen nano-capsules of the present invention plays a major role in the encapsulation of sunscreen agents, and the raspberry-shaped sunscreen nano-capsules are prepared.

[0033] (4) By compounding different types of sunscreen agents, the raspberry-shaped sunscreen nano-capsules of the present invention combine the absorption of ultraviolet light by the sunscreen agents and the scattering and reflection of the sunscreen agents by the nanoparticles, achieving a full-band and highly efficient ultraviolet protection effect for the sunscreen nano-capsules.

[0034] (5) When the raspberry-shaped sunscreen nano-capsules of the present invention are applied to sunscreen, the SPF and UVAPF values can be effectively increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to make the content of the present invention be more clearly understood, the following further describes the present invention in detail according to the specific embodiments of the present invention in combination with the drawings, wherein:

[0036] Figure 1 It is a schematic structural diagram of the raspberry-shaped sunscreen nano-capsules UVNCs of Example 1 of the present invention.

[0037] Figure 2 It is an electron micrograph of the raspberry-shaped sunscreen nano-capsules UVNCs of Example 1 of the present invention; wherein, a is a scanning electron micrograph and b is a transmission electron micrograph.

[0038] Figure 3 It is a scanning electron micrograph of SDS-UVNCs of Comparative Example 1 of the present invention.

[0039] Figure 4 It is a scanning electron micrograph of St-UVNCs of Comparative Example 2 of the present invention.

[0040] Figure 5 It is a scanning electron micrograph of UVNCs / EtOH of Comparative Example 3 of the present invention.

[0041] Figure 6 It is a scanning electron micrograph of the nano-capsules at 0.25, 0.5, 1, 2, 3, 4, 6, 8, 16, 24 h in the polymerization reaction based on Example 1 of the present invention.

[0042] Figure 7 It is a scanning electron micrograph of the nano-capsules when the mass ratio of P(St-co-MAA) to the oil-phase monomer is 0.5, 0.75, 1, 1.25 based on Example 1 of the present invention.

[0043] Figure 8 It is a high-resolution XPS spectrogram of C1s and N1s on the surfaces of UVNCs and UVNCs / EtOH of the present invention.

[0044] Figure 9 XPS spectra of UVNCs and UVNCs / EtOH with different etching times of the present invention; wherein, a is the C1s overlapping spectrum, and b is the variation diagram of N content (at%).

[0045] Figure 10 The ultraviolet absorption spectra of UVNCs, UVNCs / EtOH, DHHB, OD-PABA and P(St-co-MAA) of the present invention.

[0046] Figure 11 The SPF and UVAPF values of sunscreen S1-S5 of the present invention. Detailed implementation mode

[0047] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited do not limit the present invention.

[0048] In the present invention, unless otherwise specified, the components of the base oil phase in the examples are: 0.8 g of homosalate, 1 g of isopropyl myristate, 1 g of triglyceride caprylic capric acid, 0.5 g of glycerol, 0.5 g of white oil, 0.5 g of lanolin, 0.2 g of white petrolatum, 0.2 g of lauryl PEG-9 polydimethylsiloxyethyl polydimethylsiloxane, and 0.15 g of cetearyl alcohol.

[0049] Example 1

[0050] A raspberry-shaped sunscreen nano-capsule and its preparation method specifically include the following steps:

[0051] (1) Preparation of random amphiphilic copolymer: Weigh 6.249 g of St, 3.444 g of MAA, initiator AIBN (3% of the total monomer molar amount) and 30 mL of isopropanol in a round-bottom flask, and ultrasonically dissolve the AIBN crystals completely. Deoxygenate by passing nitrogen for 30 min, place the flask in an oil bath at 65 °C and react for 24 h, with a stirring rate of 300 r / min. The polymerization product is washed several times with petroleum ether and dried in a vacuum drying oven at 45 °C for 24 h to obtain a white powdery random amphiphilic copolymer P(St-co-MAA).

[0052] (2) Preparation of random amphiphilic copolymer solution: Add 5 g of random amphiphilic polymer P(St-co-MAA) to 206.35 mL of sodium hydroxide aqueous solution (0.1 mol / L), stir and dissolve for 24 h, dilute and make up the volume to 500 mL, and then obtain a 10 g / L P(St-co-MAA) solution as the aqueous phase of the miniemulsion system.

[0053] (3) Preparation of the oil phase: Weigh 0.5327 g of EGDMA, 0.0673 g of MMA, 0.2 g of DHHB, and 0.1 g of OD-PABA in a 100 mL beaker. The initiator AIBN is 3% of the total molar amount of EGDMA and MMA. Place the beaker in an ultrasonic environment and shake until the solids are completely dissolved to obtain the oil phase of the miniemulsion system.

[0054] (4) Preparation of the oil-in-water (O / W) miniemulsion: Take 60 mL of the P(St-co-MAA) solution and mix it with the above-mentioned oil phase. Stir in an ultrasonic environment for pre-emulsification until there are no obvious large-sized oil droplets in the system. Then, use a ultrasonic cell disruptor with a power of 300 W to ultrasonically miniemulsify for 2 min to obtain the oil-in-water (O / W) miniemulsion.

[0055] (5) Preparation of raspberry-shaped sunscreen nanocapsules: Transfer the oil-in-water (O / W) miniemulsion into a 100 mL three-necked flask. Purge with nitrogen for 30 min and then place it in a water bath at 65 °C. The mechanical stirring speed is 350 r / min, and the polymerization reaction is carried out for 24 h. The reaction solution is centrifuged at 5000 r / min for 5 min. The lower layer precipitate is washed with petroleum ether multiple times until no absorption peak of the organic ultraviolet absorber can be detected in the washing solution. The lower layer precipitate is dried in a vacuum at 40 °C to obtain raspberry-shaped sunscreen nanocapsules (UVNCs), as Figure 1 shown.

[0056] Example 2

[0057] A kind of raspberry-shaped sunscreen nanocapsule and its preparation method specifically include the following steps:

[0058] Basically the same as Example 1, the main difference is the preparation of the random amphiphilic copolymer in step (1): Weigh 5.271 g of St, 4.304 g of MAA, the initiator AIBN (3% of the total monomer molar amount), and 30 mL of isopropanol in a round-bottom flask. Ultrasonic until the AIBN crystals are completely dissolved. Purge with nitrogen for 30 min, place the flask in an oil bath at 65 °C and react for 24 h, with a stirring rate of 300 r / min. The polymerization product is washed with petroleum ether several times and dried in a vacuum drying oven at 45 °C for 24 h to obtain a white powdery amphiphilic random copolymer P(St-co-MAA).

[0059] Example 3

[0060] A kind of raspberry-shaped sunscreen nanocapsule and its preparation method specifically include the following steps:

[0061] Basically the same as Example 1, the main difference is as follows: Preparation of the random amphiphilic copolymer in step (1): Weigh 4.166 g of St, 5.1654 g of MAA, initiator AIBN (3% of the total monomer molar amount), and 30 mL of isopropanol in a round-bottom flask, and ultrasonicate until the AIBN crystals are completely dissolved. Purge with nitrogen for 30 min, place the flask in an oil bath at 65 °C and react for 24 h with a stirring rate of 300 r / min. Wash the polymerization product several times with petroleum ether and dry it in a vacuum drying oven at 45 °C for 24 h to obtain a white powdery random amphiphilic copolymer P(St-co-MAA).

[0062] Comparative Example 1

[0063] Basically the same as Example 1, the difference is that 60 mL of an aqueous solution of P(St-co-MAA) (10 g / L) in step (1) is replaced with 60 mL of an aqueous solution of sodium dodecyl sulfate (SDS) (2 g / L, lower than the CMC concentration) to prepare SDS-UVNCs.

[0064] Comparative Example 2

[0065] Basically the same as Example 1, the difference is that the polymerization monomers in step (2) are changed from MMA and EGDMA to St to prepare St-UVNCs.

[0066] Comparative Example 3

[0067] Basically the same as Example 1, the difference is that petroleum ether in step (4) is replaced with absolute ethanol to prepare UVNCs / EtOH.

[0068] Test Example 1: Morphology analysis

[0069] (1) Observe the nanocapsules prepared in Example 1 and Comparative Examples 1-4 under a scanning electron microscope or a transmission electron microscope, and the results are shown in Figures 2-5. As Figure 2 can be seen, the obtained particles have a rough surface, and the overall raspberry-like structure shows a relatively wide particle size distribution. Compared with Example 1, the nanocapsules prepared in Comparative Examples 1-3( Figures 3 - 5 ) have a smooth surface or a smaller surface roughness. This raspberry structure is related to the self-assembly behavior of P(St-co-MAA) on the surface of the nanocapsules. The nanocapsule structure includes a core formed by P(MMA-EGDMA) polymer particles and a raspberry-like outer shell layer formed by self-assembled aggregates of P(St-co-MAA). Washing with absolute ethanol can destroy the raspberry structure on the surface of the nanocapsules, but does not destroy the internal P(MMA-EGDMA) polymer microspheres.

[0070] (2) Based on Example 1, continuous sampling was carried out on the miniemulsion reaction system of the same batch to observe the formation process of raspberry-shaped sunscreen nanocapsules. The SEM images of the sunscreen nanocapsules at different polymerization times are as follows Figure 6 shown. As can be seen from Figure 6 , when the polymerization time was 0.25 h, the surface of the particles was relatively smooth, without small protrusions and rough morphologies ( Figure 6 a). As the reaction proceeded, the rough surface gradually became obvious ( Figure 6 b - 6c). When the polymerization reaction reached 2 h, the raspberry-shaped nanocapsules with clear contours were basically formed ( Figure 6 d). By the reaction time of 4 h, the raspberry-shaped structure was the most obvious ( Figure 6 d - 6f). Thereafter, within the reaction time of 6 - 24 h, the protrusions and roughness on the surface hardly changed ( Figure 6 g - 6j). These small raspberry particles only existed on the surface of the nanocapsules and were not found in the background of the SEM images, indicating that this raspberry-shaped structure did not come from the deposition or condensation between heterogeneous particles, but was gradually formed on the surface of the nanocapsules.

[0071] (3) Based on Example 1, the SEM images of the sunscreen nanocapsules were observed when the mass ratios of different P(St - co - MAA) to the oil-phase monomer were 0.5, 0.75, 1, and 1.25. The results are as follows Figure 7 shown. As can be seen from Figure 7 , when the mass ratio of P(St - co - MAA) to the oil-phase monomer increased from 0.5 to 1.25, the raspberry structure of the sunscreen nanocapsules became more obvious.

[0072] Test Example 2: Encapsulation Efficiency Analysis

[0073] (1) The addition amount of P(St - co - MAA) had a great influence on the encapsulation efficiency of the sunscreen agent. Based on Example 1, when the mass ratio of the added P(St - co - MAA) to the oil-phase monomer increased from 0.25 to 1.50, the encapsulation efficiencies of DHHB and OD - PABA increased from 25.96% and 16.21% to 72.43% and 64.69%, respectively.

[0074] In addition to the morphological differences, the encapsulation efficiencies of DHHB and OD - PABA for the UVNCs obtained by washing with petroleum ether were 72.43% and 64.69%, and the total encapsulation efficiency was 69.85%. While the corresponding values for the UVNCs / EtOH obtained by washing with absolute ethanol were 21.18%, 18.89%, and 20.44%, respectively. The total encapsulation efficiency of the sunscreen agent of the UVNCs was approximately 3.42 times that of the UVNCs / EtOH.

[0075] The SDS-UVNCs have a smooth surface without raspberry structure, and their encapsulation efficiency is not significantly affected by the solvent. The total encapsulation efficiencies measured by petroleum ether and absolute ethanol are 27.37% and 24.22% respectively, which are similar to the results of UVNCs / EtOH, but both are much lower than those of UVNCs.

[0076] Test Example 3: XPS Analysis

[0077] (1) Use an X-ray energy spectrometer to perform surface analysis and depth profiling on the UVNCs prepared in Example 1 and the UVNCs / EtOH prepared in Comparative Example 3. Figure 8 are the high-resolution spectra of C1s and N1s for both. From Figure 8 it can be seen that since the outer layer of the P(St-co-MAA) self-assembled aggregate is the MAA layer, covering the internal St hydrophobic core, the π-π* satellite peak with a binding energy of 291.22 eV is not found on the surface of UVNCs. At this time, the binding energy of the detected C-O bond absorption peak is 285.93 eV. After washing with absolute ethanol, the P(MMA-EGDMA) polymer particles inside the nanocapsules and the remaining St on their surface are exposed. Therefore, the π-π* satellite peak at 291.2 eV can be detected on the surface of UVNCs / EtOH. The binding energy of the C-O bond in P(EGDMA) is 286.6 eV, while the binding energy of the C-O bond in UVNCs / EtOH is 286.42 eV, which is 0.49 eV higher than that of UVNCs, indicating that a large amount of EGDMA exists on the surface of UVNCs / EtOH. The N1s binding energies on the surfaces of UVNCs and UVNCs / EtOH are 399.91 eV and 400.26 eV respectively. This N1s around 400 eV belongs to the tertiary amino group directly connected to the benzene ring in the DHHB and OD-PABA molecular structures. The nitrogen content (At (N) , at%) of UVNCs is 1.12%, which is 1.87 times that of UVNCs / EtOH.

[0078] (2) Press the solid powders of the UVNCs prepared in Example 1 and the UVNCs / EtOH prepared in Comparative Example 3 into tablets for depth profiling. The results are as Figure 9 shown. From Figure 9 a, it can be seen that as the etching time increases, the C1s peak shape of UVNCs gradually changes from "short and wide" to "tall and narrow", and the surface layer MAA is etched away layer by layer, and the relative content of the corresponding C-O bond decreases. In contrast, the change of the C1s spectrum of UVNCs / EtOH has no regular pattern. The change of At (N) under different etching times is as Figure 9 shown in b. When not etched, the At (N) on the surface of UVNCs / EtOH is 0.6%, and it remains basically unchanged at 120 s, while after 240 s, At(N) It drops to about 0.4%. Since the St segment of P(St-co-MAA) is embedded in the monomer droplets, and part of the St will be used as an anchor point to fix the subsequent self-assembled aggregates of P(St-co-MAA), there is a St-rich layer on the surface of UVNCs / EtOH. Due to the π-π electronic interaction, the relative content of the sunscreen and At (N) is slightly higher than that inside the UVNCs / EtOH particles. Similarly, the hydrophobic core of the self-assembled aggregates of St is more likely to encapsulate the sunscreen. After removing the surface hydrophilic layer of MAA by multi-layer etching, the At of UVNCs (N) increases from 1.12% to 1.27%.

[0079] The etched area of the XPS depth profiling experiment is 300×700μm 2 , which is much larger than the cross-sectional area of a single sunscreen nanocapsule, and the sizes of the particles are uneven. Therefore, At (N) actually corresponds to the average value of all nanocapsules in this etched layer. The surface analysis and depth profiling results of the nanocapsules by XPS show that the ratio of At of UVNCs to UVNCs / EtOH (N) ranges from 1.87 to 3.10, further proving the uneven distribution of the sunscreen in the raspberry-like nanocapsules. Combining the encapsulation efficiency analysis results, about 49.41% of the sunscreen is coated by the self-assembled aggregates of P(St-co-MAA), while the total encapsulation efficiency of the P(MMA-EGDMA) polymer particles for the sunscreen is about 20.44%. The distribution ratio of the sunscreen between the outer shell and the inner core is 2.42:1.

[0080] Test Example 4: Analysis of UV protection performance

[0081] (1) The solid UV reflection spectra of UVNCs prepared in Example 1, UVNCs / EtOH prepared in Comparative Example 3, DHHB, OD-PABA, and P(St-co-MAA) were measured by an ultraviolet-visible spectrophotometer, and the results are as Figure 10 shown. It can be seen from Figure 10 comparing the absorption curves of DHHB and OD-PABA that both UVNCs and UVNCs / EtOH can achieve UV protection in the full wavelength range (200nm - 400nm), and the protection effect of UVNCs is better.

[0082] (2) Preparation of Sunscreens S1 - S5: Respectively add blank (without adding microcapsules), 0.3 g of DHHB plus 0.14 g of OD - PABA, 1 g of UVNCs / EtOH prepared in Comparative Example 3, 1.31 g of DHHB plus 0.58 g of OD - PABA, and 1 g of UVNCs prepared in Example 1 into the base oil phase. Melt at 80 °C, add deionized water, and homogenize and disperse at a speed of 8000 r / min for 3 min using a high - speed shear homogenizer to obtain 10 g of sunscreens S1 - S5.

[0083] The SPF and UVAPF values of S1 - S5 were tested, and the results are as Figure 11 shown. As Figure 11 can be seen, the sun protection factors SPF and UVAPF values of S5 are 58.8 and 6.32 respectively, which are approximately 194.1% and 140.0% of the corresponding values of S4. The sun protection factors SPF and UVAPF values of S3 are 23.7 and 4.03 respectively, which are approximately 153.9% and 120.6% of the corresponding values of S2. Both UVNCs and UVNCs / EtOH show better ultraviolet protection than free sunscreens with the same loading amount. The effect of UVNCs on improving the sun protection factor is higher than that of UVNCs / EtOH. On the one hand, the rough surface may be more conducive to scattering and reflecting ultraviolet rays. On the other hand, this surface encapsulation is more conducive to improving the ultraviolet absorption efficiency of the sunscreens.

[0084] Obviously, the above - mentioned embodiments are only examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or alterations derived therefrom are still within the protection scope of this invention.

Claims

1. A raspberry-shaped sunscreen nano-capsule, characterized in that, it comprises a random amphiphilic copolymer solution, a sunscreen agent, an oil-phase monomer and an initiator; the concentration of the random amphiphilic copolymer solution is 8 g / L - 12 g / L; the mass ratio of the sunscreen agent to the oil-phase monomer is 1:1.8 - 2.2; the content of the initiator is 1% - 5% of the molar amount of the oil-phase monomer; the mass ratio of the random amphiphilic copolymer to the oil-phase monomer in the random amphiphilic copolymer solution is 0.5 - 1.25:1; the random amphiphilic copolymer is obtained by copolymerization of styrene and methacrylic acid in a molar ratio of 2:8 - 8:2 under the action of azobisisobutyronitrile through solution radical polymerization; the sunscreen agent is obtained by mixing ethylhexyl dimethyl PABA and diethylamino hydroxybenzoyl hexyl benzoate in a mass ratio of 1:1 - 3; the oil-phase monomer is obtained by mixing methyl methacrylate and ethylene glycol dimethacrylate in a molar ratio of 1:1 - 5; wherein, the raspberry-shaped sunscreen nano-capsule has a self-assembled aggregate of the random amphiphilic copolymer as the outer shell layer and a polymer microsphere formed by polymerization of the oil-phase monomer as the core; the sunscreen agent is encapsulated in both the outer shell layer and the core; the surface of the raspberry-shaped sunscreen nano-capsule presents a raspberry-shaped structure.

2. The raspberry-shaped sunscreen nano-capsule according to claim 1, characterized in that, the initiator is azobisisobutyronitrile.

3. The raspberry-shaped sunscreen nano-capsule according to claim 1, characterized in that, the solvent of the random amphiphilic copolymer solution is sodium hydroxide solution.

4. The raspberry-shaped sunscreen nano-capsule according to claim 3, characterized in that, the concentration of the sodium hydroxide solution is 0.05 mol / L - 0.2 mol / L.

5. The preparation method of the raspberry-shaped sunscreen nano-capsule according to any one of claims 1 - 4, characterized in that, it comprises the following steps, (1) Dissolve the random amphiphilic copolymer in sodium hydroxide solution to obtain a random amphiphilic copolymer solution; (2) Mix the sunscreen agent, the oil-phase monomer and the initiator evenly to obtain an oil phase; (3) Add the random amphiphilic copolymer solution described in step (1) to the oil phase described in step (2), and through pre-emulsification and fine emulsification, obtain an oil-in-water type fine emulsion; (4) Under a nitrogen atmosphere, the oil-in-water type fine emulsion described in step (3) undergoes a polymerization reaction, and after washing and centrifugation, obtain the described raspberry-shaped sunscreen nano-capsule.

6. The preparation method of the raspberry-shaped sunscreen nano-capsule according to claim 5, characterized in that, in step (4), the temperature of the polymerization reaction is 60°C - 70°C and the time is 12 h - 24 h.

7. A sunscreen, characterized in that, the sunscreen is prepared from the raspberry-shaped sunscreen nano-capsule according to any one of claims 1 - 4.

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