UV shielding agent and method for producing the same

Abstract

The present invention provides an ultraviolet shielding agent containing spherical silicon nanocrystals of a predetermined particle size. The agent contains spherical silicon nanocrystals with a peak particle size distribution between 40 nm and 200 nm. Particularly, it is preferable to include silicon nanocrystals between 60 nm and less than 90 nm. The agent has an ultraviolet transmittance of 10% or less at 400 nm and below, a visible light transmittance of 50% or more at 500 nm and above, and a haze value of 40% or more at 500 nm and below. The ultraviolet shielding agent is in the form of a dispersion or film containing silicon nanocrystals with a controlled particle size distribution.

Description

Technical Field

[0001] The present invention relates to a technique for using silicon nanocrystals as an ultraviolet shielding agent.

Background Art

[0002] Conventionally, titanium oxide and zinc oxide have been used as nanoparticles for ultraviolet shielding in applications such as cosmetics (sunscreens, foundations, skin care products, facial cleansers, etc.) for the purpose of ultraviolet (UV) cut. In particular, it is an ultraviolet scattering agent that physically scatters and reflects ultraviolet rays, and has a function of uniformly covering the skin and reflecting and scattering ultraviolet rays on the skin surface to prevent the influence of ultraviolet rays. On the other hand, there are problems with the carcinogenicity of titanium oxide and its performance as an ultraviolet shielding agent. In order to enhance the ultraviolet shielding effect, it is necessary to increase the particle size, but the light scattering in the visible region also increases, resulting in a loss of transparency, so the applications are limited.

[0003] In the present invention, silicon nanocrystals are used as an ultraviolet shielding agent. As a technique using silicon nanocrystals, a hydrogen supply material including silicon fine particles and a medium in contact with the silicon fine particles is known (see Patent Document 1). In Patent Document 1, as a typical product example that can adopt the structure of each embodiment, there is a disclosure of "cosmetics for ultraviolet protection" (paragraph 0065), but the silicon fine particles are only used as a hydrogen supply material and are not used as an ultraviolet shielding agent.

[0004] Also, regarding a method for manufacturing fine particles of an ultraviolet shielding material, a technique of immersing a zinc oxide precursor in an alcohol solution containing silicon is known (see Patent Document 2). However, the manufacturing method of Patent Document 2 uses zinc oxide and does not use silicon nanocrystals as an ultraviolet shielding agent.

[0005] The present inventors have already proposed a highly opaque nanoparticle film with a thickness of 100 to 220 nm containing inorganic nanoparticles with a refractive index of 3 or higher, having a reflectance of 60% or more and a transmittance of 20% or less in the visible light region (see Patent Document 3). This is because single-layer, double-layer, or triple-layer particle films using inorganic nanoparticles (diameter 100 to 220 nm) with a refractive index of 3 or higher have high opacity. By using nanoparticles with different particle size distributions, high opacity and hue adjustment can be achieved simultaneously, and the film thickness is approximately the diameter of the nanoparticles, while the transmittance in the visible light region can be suppressed to 20% or less. However, the technology in Patent Document 3 does not use silicon nanocrystals as an ultraviolet shielding agent. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Re-tabled publication 2018 / 037818 [Patent Document 2] Japanese Patent Publication No. 2009-132599 [Patent Document 3] Japanese Patent Publication No. 2024-027742 [Overview of the project] [Problems that the invention aims to solve]

[0007] Titanium dioxide, a UV-blocking agent found in conventional sunscreens and skincare products, has raised concerns about its carcinogenicity. On the other hand, silicon has high UV absorption capacity as a material, and by creating nanoparticles of several tens of nanometers in size, the combined effects of scattering and absorption enhancement through Mie resonance may result in even higher UV absorption capacity. The inventors focused on the changes in refractive index in the ultraviolet region, the spectral characteristics of silicon nanocrystals, such as their superior ultraviolet absorption efficiency compared to other materials like titanium dioxide and zinc oxide, and the biocompatibility of silicon nanocrystals, and completed the present invention. In view of these circumstances, the present invention aims to provide an ultraviolet shielding agent containing spherical silicon nanocrystals of a predetermined particle size. [Means for solving the problem]

[0008] To solve the above problems, the ultraviolet shielding agent of the present invention is characterized by containing silicon nanocrystals that are spherical in shape and have a particle size distribution peak value in the range of 40 nm to less than 90 nm. The inventors have achieved ultraviolet scattering and absorption effects with smaller particle sizes by using silicon nanocrystals with a higher refractive index than titanium dioxide. By controlling the particle size distribution peak value within the range of 40 nm to less than 90 nm, with a high refractive index for ultraviolet light in the 300-400 nm range, Mie resonance is induced in the ultraviolet region, shielding ultraviolet light while maintaining transmittance in the visible range. The particle size distribution is controlled to ±20%. High scattering and absorption efficiency is observed for ultraviolet light in the 300-400 nm range, and when a particle film is formed, the transmittance in the 300-400 nm range is remarkably low, achieving ultraviolet shielding. In this specification, transmittance refers to diffuse transmittance.

[0009] Spherical silicon nanocrystals with a particle size distribution peak value between 40 nm and 90 nm have an excellent attenuation spectrum (sum of absorption and scattering) for ultraviolet light below 400 nm, particularly long-wave ultraviolet light (hereinafter referred to as UVA) with wavelengths of 320-400 nm, and can therefore be used as an ultraviolet shielding agent. Furthermore, for medium-wave ultraviolet light (hereinafter referred to as UVB) with wavelengths of 290-320 nm, which has approximately 1000 times the effect on the skin of UVA, the ultraviolet shielding agent of the present invention has an attenuation spectrum that shows higher absorption and scattering efficiency for ultraviolet light in the 300-320 nm range compared to titanium dioxide, which is currently used as a countermeasure against UVB. Furthermore, the ultraviolet shielding agent of the present invention consists of silicon nanocrystals that are spherical in shape and have a particle size distribution peak value in the range of 40 nm to less than 90 nm. Note that particle size refers to the average particle size, and particle size distribution is the range obtained by dividing the standard deviation by the average particle size. In particular, it is preferable that the peak value range of the particle size distribution of the silicon nanocrystals is 60 to less than 90 nm. Silicon nanocrystals having such a peak value range particle size distribution have an excellent attenuation spectrum in the 375 to 400 nm range. Therefore, they can efficiently block UVA.

[0010] In the case of the UV shielding agent of the present invention, the transmittance of ultraviolet light below 400 nm is 10% or less. Alternatively, in the case of the UV shielding agent of the present invention, the UV transmittance below 400 nm is 10% or less, and the visible light transmittance above 500 nm is 50% or more. In addition, the haze value below 500 nm is 40% or more. For UV light below 400 nm, the transmittance is 20% or less, but the haze value is high at 60% or more.

[0011] The form of the UV shielding agent of the present invention is a dispersion containing silicon nanocrystals with a controlled particle size distribution. Alternatively, the form of the UV shielding agent of the present invention is a film containing silicon nanocrystals, which may be a single-layer film or a multilayer film.

[0012] The ultraviolet shielding agent of the present invention is a laminated structure comprising a first layer containing spherical silicon nanocrystals with a peak particle size distribution between 40 nm and less than 90 nm, and a second layer containing spherical silicon nanocrystals with a peak particle size distribution between 100 nm and 220 nm. The lamination order may be such that the second layer is laminated on top of the first layer, or conversely, the first layer is laminated on top of the second layer. There may also be three or more layers; for example, the first layer may be laminated on top of the second layer, and then the second layer on top of that. The first layer containing silicon nanocrystals in the range of 40 nm and less than 90 nm refers to a single, two-layer, or three-layer multilayer film formed of silicon particles with substantially uniform particle sizes. Alternatively, it may be a mixed layer containing at least two types of silicon particles with different particle sizes. The second layer containing silicon nanocrystals in the range of 100 nm and 220 nm is similar. When achieving a layer thickness with a single particle size, in the case of a single layer, the particle size (diameter) is made uniform, and the thickness is equal to that particle size. In the case of two layers, the particle diameter (diameter) is made uniform, and the thickness is equal to twice that particle diameter. When achieving a layer thickness with two or more particle sizes, the thickness is adjusted by mixing different particle sizes. The first layer, containing silicon nanocrystals in the range of 40nm to less than 90nm, blocks ultraviolet light, while the second layer, containing silicon nanocrystals in the range of 100 to 220nm, scatters visible light and produces color.

[0013] The ultraviolet shielding agent of the present invention is a mixture of spherical silicon nanocrystals with a peak particle size distribution between 40 nm and less than 90 nm and spherical silicon nanocrystals with a peak particle size distribution between 100 nm and 220 nm. This configuration consists of a mixture of small silicon nanocrystals with a particle size between 40 nm and less than 90 nm and large silicon nanocrystals with a particle size between 100 nm and 220 nm. Small silicon nanocrystals with a particle size between 40nm and 90nm block ultraviolet light, while larger silicon nanocrystals with a particle size between 100nm and 220nm scatter visible light and emit color.

[0014] The ultraviolet shielding agent of the present invention may be a dispersion containing silicon nanocrystals with a spherical shape and a peak particle size distribution within the range of 90 nm to 200 nm. Alternatively, the ultraviolet shielding agent of the present invention may be a powder containing silicon nanocrystals with a spherical shape and a peak particle size distribution within the range of 90 nm to 200 nm. Dispersions and powders containing silicon nanocrystals with a spherical shape and a peak particle size distribution within the range of 90 nm to 200 nm have a lower diffuse transmittance in the ultraviolet region of 290 to 400 nm compared to the visible light region, and thus have an ultraviolet shielding effect.

[0015] The cosmetic products of the present invention contain the ultraviolet shielding agent of the present invention and have a transmittance of 20% or less for ultraviolet rays below 400 nm. Conventionally, titanium dioxide (white) and iron oxide (yellow, red, black) have been used as inorganic pigments in cosmetic products (foundation, facial cleanser, etc.), but titanium dioxide and the like do not have sufficient opacity, so it was necessary to incorporate them in large quantities (>10%) into cosmetic products. However, incorporating large quantities of inorganic pigments leads to problems such as a heavy feel when applying the cosmetic product and a feeling of tightness in the skin after the cosmetic product dries. In addition, in the case of cosmetic products intended to block ultraviolet rays (sunscreen, facial cleanser, etc.), titanium dioxide is also used as ultraviolet shielding nanoparticles, and titanium dioxide physically reflects and scatters ultraviolet rays on the skin surface, preventing the effects of ultraviolet rays. However, in the case of titanium dioxide, there are concerns about carcinogenicity and problems such as the fact that the performance as an ultraviolet shielding agent cannot be ensured unless the particle size is large. In the present invention, by incorporating silicon nanocrystals as an inorganic pigment in a predetermined amount into cosmetic products, cosmetic products with higher opacity than titanium dioxide, even in small amounts, are realized, achieving higher shielding power against ultraviolet rays compared to titanium dioxide.

[0016] The cosmetic product of the present invention preferably contains 0.05% by weight or more of the ultraviolet shielding agent of the present invention. If the silicon nanocrystal content is 0.05% by weight or more, there is a difference in opacity compared to titanium dioxide, and there is a difference in diffuse transmittance for ultraviolet light in the 300-400 nm range. However, if the silicon nanocrystal content is less than 0.05% by weight (for example, a content of 0.01% by weight), no difference in opacity compared to titanium dioxide can be observed, and no difference in diffuse transmittance for ultraviolet light can be observed.

[0017] In the case of the cosmetic product of the present invention, it is more preferable that the silicon nanocrystal content is 0.2% by weight or more and 10% by weight or less. If the silicon nanocrystal content is 0.2% by weight or more, there is a significant difference in opacity compared to titanium dioxide, and there is also a significant difference in ultraviolet light at 300-400 nm. Even if the silicon nanocrystal content is 0.05% by weight or more and less than 0.2% by weight, it has superior opacity compared to titanium dioxide, but if the silicon nanocrystal content is 0.2% by weight or more and 10% by weight or less, an even more significant opacity can be obtained. Furthermore, the reason for limiting the silicon nanocrystal content to 10% by weight or less is to avoid problems such as the heavy feel of the cosmetic product when applied, or the feeling of tightness on the skin after the cosmetic product dries, which can occur if a large amount (>10%) of inorganic pigments is included.

[0018] In the case of the cosmetic product of the present invention, it is even more preferable that the silicon nanocrystal content is 0.5% by weight or more and 5% by weight or less. If the content is 0.5% by weight or more, there is a significant difference in opacity compared to titanium dioxide or large-particle (particle size of about 1000 nm) silicon powder, and there is also a significant difference in diffuse transmittance to ultraviolet light with a wavelength of 300 to 400 nm. Even if the silicon nanocrystal content is less than 0.5% by weight, it has the same opacity as large-particle silicon powder and the same diffuse transmittance to ultraviolet light. Furthermore, the reason for limiting the content to 5% by weight or less is that, compared to a content of 10% by weight or less, the amount of inorganic pigment is smaller, resulting in a lighter feel when applying cosmetics and less of a squeaky sensation after drying.

[0019] Specifically, when the film thickness of the cosmetic product of the present invention is 50 μm, the diffuse transmittance in the ultraviolet region is less than 5%, and the hiding power at visible light wavelengths is 50% or more. The cosmetic product of the present invention has a diffuse transmittance in the ultraviolet region of less than 5%, and the diffuse transmittance in the ultraviolet region is smaller than that of titanium dioxide nanoparticles having an average particle size of 200 nm. In addition, the hiding power at visible light wavelengths is 50% or more. As will be described later, when the content of silicon nanocrystals is 0.5 wt%, 2 wt%, or 5 wt%, measurement results show that the hiding power is about 100%, indicating an extremely high hiding power compared to titanium dioxide. Even when the content of silicon nanocrystals is 0.05 wt%, a measurement result of a hiding power of 44% is obtained, indicating a higher hiding power than the hiding power of 29% of titanium dioxide.

[0020] Next, a method for producing an ultraviolet light shielding agent will be described. The method for producing an ultraviolet light shielding agent of the present invention includes the following steps a) to e). a) A step of using silicon monoxide powder as a raw material and performing annealing treatment on the silicon monoxide powder from a temperature lower than the melting point of elemental silicon to a temperature higher than the melting point. Here, the melting point of elemental silicon is 1414 °C, but the annealing treatment is performed under temperature conditions higher than 1414 °C to grow silicon nanocrystals. In the annealing treatment, it is also possible to control the particle size of the silicon nanocrystals by controlling the temperature conditions. When the annealing treatment is performed at a temperature higher than the melting point of elemental silicon, a sharp increase in particle size and a shape change such as a significant improvement in roundness occur before and after exceeding the melting point. b) A step of etching the annealed powder (particles of silicon dioxide containing silicon nanocrystals) using an etching solution. c) After etching, a step of replacing the etching solution with a polar solvent (such as methanol). d) A step of stirring in a polar solvent to disperse the silicon nanocrystals. e) A step of separating the particle size of silicon nanocrystals in a dispersion of silicon nanocrystals and adjusting the particle size distribution in the dispersion to a target particle size within the range of 40 nm to less than 90 nm. The step of standardizing the particle size to the target size specifically involves using density gradient centrifugation or particle size sorting by adding a poor solvent. When using density gradient centrifugation, it is best to centrifuge the dispersion in a centrifuge tube lying horizontally to achieve high particle size resolution. By centrifugation in the horizontal direction with the centrifuge tube lying horizontally, the direction of the centrifugal force and the longitudinal direction toward the bottom of the centrifuge tube become the same, increasing the sedimentation path length and thus improving the resolution of density gradient centrifugation.

[0021] In another embodiment, the method for producing the ultraviolet shielding agent of the present invention comprises steps a) to d) above, and further comprises steps f) and g), wherein silicon nanocrystals with a particle size of 100 nm or more are etched to standardize the particle size. f) A step of separating the particle size of silicon nanocrystals in a dispersion of silicon nanocrystals and adjusting the peak value of the particle size distribution in the dispersion to match the particle size of an intermediate target in the range of 90 nm or more. g) Etching silicon nanocrystals of intermediate target particle size to adjust the target particle size so that the peak value of the particle size distribution in the dispersion is within the range of 40 nm to less than 90 nm. Since it is known that the hue of a silicon nanocrystal dispersion is orange when the particle size is 90-100 nm, pink when it is 100-110 nm, blue when it is 115-125 nm, and green when it is 130-140 nm, first the particle size is adjusted to an intermediate target particle size in the range of 90 nm or more, and then etching is performed to adjust the particle size to a target particle size where the peak value of the particle size distribution in the dispersion is in the range of 40 nm to less than 90 nm.

[0022] In this process, etching is preferably carried out by immersing silicon nanocrystals in a solution of nitric acid or hydrogen peroxide and hydrogen fluoride. The etching time and the concentration of nitric acid, etc., are controlled in order to produce the target particle size.

[0023] Next, the method for producing the UV-blocking agent for cosmetic products of the present invention will be described. The method for producing the UV-blocking agent for cosmetic products of the present invention comprises the following steps a) and b). a) Particle size adjustment step: The particle sizes of silicon nanocrystals in the dispersion are separated, and the peak values ​​of the particle size distribution in the dispersion are adjusted to match the particle size corresponding to the color of the target pigment, within the range of 40 nm to 200 nm. Silicon nanocrystals are grown by annealing under temperature conditions higher than the melting point of elemental silicon. The annealed powder is etched, and after etching, the etching solution is replaced with a polar solvent. Subsequently, in a dispersion of polar solvent, the particle size is standardized to a target size within the range of 40 nm to less than 90 nm in the particle size distribution peak value by density gradient centrifugation or similar methods.

[0024] b) Content adjustment step: The prepared pigments are dispersed in a pigment dispersion, and the emulsifier in the cosmetic product and the pigment dispersion are mixed to adjust the content of silicon nanocrystals. A pigment dispersion is a liquid in which colored powdered pigments are dispersed to prevent particle aggregation and ensure uniform dispersion of the pigments, thereby achieving even color development. In cosmetic products, isopropanol, for example, is preferably used. Cosmetic products are a mixture of an emulsifier, which consists of an oil phase and an aqueous phase, and a pigment dispersion.

[0025] Furthermore, the hue of silicon nanocrystal pigment dispersions, whose hue is changed by controlling the peak value of the particle size distribution to be between 40 nm and 200 nm and the particle size distribution (range obtained by dividing the standard deviation by the average particle size) to ±10-15%, is as follows: for example, if the average particle size is 60-80 nm, the hue will be yellow; if it is 80-100 nm, the hue will be orange; if the particle size is 100-110 nm, the hue will be pink; if it is 115-125 nm, the hue will be blue; if it is 130-140 nm, the hue will be green; if it is 145-160 nm, the hue will be yellow; and if it is 165-200 nm, the hue will be skin tone. [Effects of the Invention]

[0026] The UV shielding agent of the present invention has the effect of efficiently absorbing ultraviolet light in the 300-400 nm range compared to existing UV shielding agents such as titanium dioxide and zinc oxide. [Brief explanation of the drawing]

[0027] [Figure 1] Absorption spectra of silicon nanocrystals with different particle sizes [Figure 2] Correlation graph of absorption spectrum, refractive index, and extinction coefficient of silicon nanocrystals. [Figure 3] Absorption spectra of silicon nanocrystals, titanium dioxide, and zinc oxide [Figure 4] Scattering spectra of silicon nanocrystals, titanium dioxide, and zinc oxide [Figure 5] Experimental results of transmission spectra of silicon nanocrystals [Figure 6] Experimental results of absorption spectra of silicon nanocrystals [Figure 7] Schematic diagram of spectral measurement [Figure 8] Transmission spectrum of silicon nanocrystal dispersion [Figure 9] SEM image of a dispersion of silicon nanocrystals [Figure 10] Transmission spectrum and haze of silicon nanocrystal particle films [Figure 11] An example of a silicon nanocrystal particle film fabrication flow. [Figure 12] Diagram explaining the Mie Resonance [Figure 13] Scattering spectra of silicon and zinc oxide [Figure 14] Wavelength dependence of refractive index (n) and extinction coefficient (κ) of silicon nanocrystals [Figure 15] Flowchart for creating liquid foundation [Figure 16] Typical ingredient list for liquid foundations [Figure 17] Image of Si nanoparticle fabrication [Figure 18]Flowchart for the fabrication of Si nanoparticles [Figure 19] Diagram illustrating diffuse transmittance [Figure 20] Diffuse transmission spectrum 1 for wavelengths from ultraviolet to visible range [Figure 21] Diffuse transmission spectra for wavelengths from ultraviolet to visible range 2 [Figure 22] Diffuse transmission spectrum 3 for wavelengths from ultraviolet to visible range [Figure 23] This figure shows the results of a comparison of the opacity of foundations in the visible light range. [Figure 24] Diagram illustrating opacity using opacity test paper [Figure 25] Graph showing the measurement results of the opacity rate. [Figure 26] Absorption spectra of silicon nanocrystals with different particle sizes 2 [Modes for carrying out the invention]

[0028] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the scope of the present invention is not limited to the following embodiments or illustrated examples, and numerous modifications and variations are possible. [Examples]

[0029] Figure 1 shows the absorption spectra (calculated values ​​from simulation) of silicon nanocrystals separated into 10 nm increments with different average particle sizes (diameter of spherical shape) ranging from 30 to 100 nm. In the ultraviolet region below 400 nm, the nanocrystals with particle sizes of 60, 70, 80, and 90 nm exhibit superior UV absorption efficiency, with the absorption efficiency peak appearing in the 375-400 nm wavelength range. The absorption efficiency in the 375-400 nm wavelength range is 1.5-3. Furthermore, silicon nanocrystals of these particle sizes also have an absorption efficiency of around 1 in the 300-375 nm wavelength range.

[0030] Silicon nanocrystals with a positive dielectric constant are known to exhibit Mie resonance in a spherical shape. Mie resonance is a phenomenon in which, as shown in Figure 12, when light of wavelength λ (nm) is incident on a material (refractive index n), the effective wavelength in the material becomes λ / n (nm). When the effective wavelength of light λ / n (nm) becomes equal to the particle size D (nm), a standing wave is formed, and the lowest-order Mie resonance, i.e., electrical and magnetic dipole resonance, appears in the optical region. In other words, the condition for the lowest-order resonance is λ / n ≈ D, and its resonance wavelength is n × D (nm). The values ​​calculated from the above simulation are based on Mie theory, which provides analytical solutions for the optical response of a sphere.

[0031] As shown in Table 1 below, the refractive index of silicon nanocrystals is higher than that of titanium dioxide, zinc oxide, and zirconium oxide, which are used as UV shielding agents. Figure 13 shows the scattering spectra of silicon nanocrystals (refractive index 4, particle size 150 nm) and zinc oxide (refractive index 2, particle size 300 nm). Due to the effect of Mie resonance, silicon nanocrystals exhibit two peaks in the visible region (400-800 nm).

[0032] [Table 1]

[0033] It should be noted that the refractive index values ​​in Table 1 above are for light with a wavelength of 600 nm. In other words, in the case of silicon nanocrystals, the refractive index value changes significantly with wavelength. Figure 14 is a graph showing the wavelength dependence of the refractive index (n) and extinction coefficient (κ) of silicon nanocrystals. The refractive index (n) of silicon nanocrystals increases as the wavelength shortens from 600 nm, and is greater than 5 in the ultraviolet region of 300-400 nm, with a peak in refractive index around 375 nm where the refractive index approaches 7. The extinction coefficient (κ) of silicon nanocrystals is negligible in the visible region, but increases sharply in the ultraviolet region of 300-400 nm, reaching about 4 at 300 nm.

[0034] Figure 2 shows a correlation graph of the absorption spectrum, refractive index, and extinction coefficient of silicon nanocrystals. The absorption spectra of silicon nanocrystals shown are those with particle sizes of 40, 50, and 60 nm, as shown in Figure 1. Generally, as the extinction coefficient (κ) increases, the absorption efficiency of the material increases. However, in Figure 2, at 350-400 nm, the peak value of the absorption efficiency of the nanocrystal decreases as the extinction coefficient (κ) increases. This is because as the extinction coefficient (κ) increases, the Mie resonance is not efficiently excited.

[0035] Figures 3 and 4 show the absorption and scattering spectra of silicon nanocrystals, titanium dioxide, and zinc oxide, respectively. The particle sizes are 40, 50, and 60 nm. From the absorption spectrum in Figure 3, it can be seen that silicon nanocrystals have a higher UV absorption efficiency compared to titanium dioxide and zinc oxide. Furthermore, the scattering spectrum in Figure 3 shows that silicon nanocrystals have higher ultraviolet scattering efficiency than zinc oxide, and that for the same particle size, silicon nanocrystals have higher ultraviolet scattering efficiency than zinc oxide.

[0036] In the above explanation, the absorption and scattering spectra were shown as calculated values ​​obtained through simulation. Figures 5 and 6 show the experimental results of the transmission and absorption spectra of silicon nanocrystals, respectively. The sample used in the experiment was a methanol solution containing silicon nanocrystals with a target particle size of 50 nm. It can be seen that the experimental results for both the transmission and absorption spectra are in general agreement with the calculated values ​​obtained through simulation (particle size of 51 nm ± 20 nm). Furthermore, Figure 5 shows that the transmittance of ultraviolet light below 400 nm is 20% or less, and Figure 6 shows that the absorbance is 0.7 or higher. For the transmittance measurement, we used a Shimadzu SolidSpec-3700i, but the measurement of diffuse transmittance itself is widely known, and any measurement and analysis device can be freely selected.

[0037] Here, the spectra in Figures 5 and 6 were obtained by irradiating a solution of silicon nanocrystals dispersed in methanol with light of each wavelength, as shown in the schematic diagram in Figure 7, and measuring the transmittance (T) = I / I0 (%) and absorbance (A) = -Log(T).

[0038] Figure 8 shows the transmission spectrum of a methanol dispersion of silicon nanocrystals with a particle size of 50 nm ± 20 nm, concentrated to approximately five times its original volume. In the methanol dispersion containing the actually prepared silicon nanocrystals, the ultraviolet transmittance below 400 nm was 10% or less, and the visible light transmittance above 500 nm was 50% or more.

[0039] Figure 9 shows an SEM image of a dispersion of silicon nanocrystals (average particle size 50 nm ± 20 nm). It can be seen that spherical silicon nanocrystals are dispersed in methanol.

[0040] Figure 10 shows the transmission spectrum and haze of a film made of silicon nanocrystals. Figure 10(1) shows a schematic diagram of a single-layer film in which only one layer of silicon nanocrystals is self-assembled on a glass substrate. Figures 10(2) and 10(3) show the total light transmittance (%) and haze (%) of the film, respectively. Similar to the dispersion, it can be seen that even with a single-layer film, the UV transmittance below 400 nm is 10% or less, and the visible light transmittance above 500 nm is 50% or more. Here, the thickness of the single-layer film is 100 nm or less. Furthermore, the haze value is 60% or more for UV light below 400 nm, and in particular, the haze value exceeds 80% for UV light in the range of 375 to 400 nm.

[0041] Figure 26(1) shows the absorption spectra (calculated values ​​from simulation) of silicon nanocrystals separated into groups with particle sizes (diameter of spherical shape) ranging from 30 to 110 nm, each with an average particle size difference of 10 nm. Figure 26(2) shows the absorption spectra (calculated values ​​from simulation) of silicon nanocrystals separated into groups with particle sizes (diameter of spherical shape) ranging from 120 to 200 nm, each with an average particle size difference of 10 nm. For silicon nanocrystals with a peak particle size distribution between 90 nm and 200 nm, the absorption spectra in the ultraviolet region of 300 to 400 nm all showed an absorption efficiency of approximately 1, indicating that they can block ultraviolet light. [Examples]

[0042] (Method for fabricating films made of silicon nanocrystals) Here, an example of a method for fabricating a film made of spherical silicon nanocrystals with controlled particle size (hereinafter also referred to as a Si nanoparticle film) will be explained with reference to Figure 11. Commercially available silicon monoxide powder is used as a raw material. The silicon monoxide powder is annealed in a nitrogen (N2) atmosphere for 30 minutes, starting at a temperature lower than the melting point of elemental silicon (1414°C) and then increasing to a temperature higher than the melting point (1350-1700°C), for example, at 1450°C (Step S1). The powder obtained after annealing is silicon dioxide particles containing silicon nanocrystals. The annealed powder is etched using hydrofluoric acid (HF) as an etching solution (Step S2). By etching with hydrofluoric acid, only the silicon dioxide portion is etched, and the silicon nanocrystals contained within the particles are extracted.

[0043] After etching, methanol is used as a polar solvent to replace the etching solution (Step S3). Then, the mixture is stirred with an ultrasonic homogenizer to disperse the silicon nanocrystals in methanol, and the particle size of the silicon nanocrystals is standardized using density gradient centrifugation (2000-3000G; 60 minutes) on the dispersion (Step S4). Density gradient centrifugation is a method of separating substances by centrifugation. In a density gradient solution in a centrifuge tube, the solution density decreases from the bottom to the top, and when a sample is centrifuged in this solution, the target substance forms a layer at a predetermined density, allowing the target substance to be separated. For example, a sucrose solution is used as the density gradient solution. When centrifugation is performed, the centrifuge tube is placed horizontally, and centrifugation is performed in the lateral direction to form layers with high particle size resolution. When the solution in the centrifuge tube is viewed with the naked eye, a gradient of color is created from the bottom to the top of the solution, and the color changes continuously. The dispersion is taken from the layer in which the particle size of silicon nanocrystals corresponding to the scattered light of the target color is standardized.

[0044] Next, silicon nanocrystals are self-assembled onto a glass substrate to form a film (Step S5). Alternatively, a transparent resin such as PVP (Polyvinylpyrrolidone), PMMA (Polymethyl methacrylate), PS (polystyrene), PET (Polyethyleneterephthalate), nylon, PE (Polyethylene), or EVA (Ethylene Vinyl Acetate Copolymer) may be added to the silicon nanocrystal dispersion, kneaded, and then the film may be formed. Through the above process, a Si nanoparticle film with controlled particle size can be produced.

[0045] In step S5 described above, the particle size of silicon nanocrystals can be reduced and standardized. Specifically, silicon nanocrystals are immersed in a solution of nitric acid (HNO3) or hydrogen peroxide (H2O2) and hydrogen fluoride (HF), and etched to standardize the particle size to a target size where the peak value of the particle size distribution in the dispersion is within the range of 40 nm to less than 90 nm. To produce the target particle size, the etching time and the concentration of nitric acid, etc., are controlled.

[0046] For example, when using nitric acid and hydrogen fluoride, silicon nanocrystals (Si) react with nitric acid to produce silica (SiO2), and then silica reacts with hydrogen fluoride to produce H2SiF6. The chemical reaction equation is shown below. Specifically, 10 mg of silicon nanocrystals is placed in a 1:1 water:methanol solution (2 mL), 1 mL of 60 wt% nitric acid and 1 mL of 46 wt% hydrogen fluoride are added, and the mixture is ultrasonically stirred for 40 minutes. After that, the solvent is replaced with alcohol by centrifugation.

[0047]

number

[0048] Figure 15 shows the production flow of a W / O (Water in Oil) type liquid foundation as a cosmetic product. Figure 16 shows typical cosmetic ingredients for liquid foundation (W / O type). As shown in Figure 16, a typical liquid foundation (W / O type) consists of an oil phase composed of PEG-10 dimethicone, cyclopentasiloxane, and disteardimonium hectorite; an aqueous phase composed of phenoxyethanol, BG (butylene glycol), glycerin, sodium chloride, ethylenediaminetetraacetic acid (EDTA) disodium, and purified water; and a pigment dispersion of isopropanol in which inorganic pigments are dispersed. In this example, silicon nanocrystals (hereinafter also referred to as Si nanoparticles) with a peak particle size distribution between 40 nm and less than 90 nm were used as the inorganic pigment. Comparative Example 1 used Si powder with an average particle size of 1000 nm (1 μm), and Comparative Example 2 used pigment-grade titanium dioxide (average particle size of 200 nm). The inorganic pigments Si nanoparticles (Example), Si powder (Comparative Example 1), and titanium dioxide (Comparative Example 2) were blended to produce samples with weight percentages of 0.01, 0.05, 0.5, 2.0, and 5.0 relative to the total cosmetic product components.

[0049] As shown in the production flow in Figure 15, the oil phase components of the cosmetic product were uniformly dispersed in a homomixer (step S01), and the uniformly dissolved aqueous phase was stirred and mixed with the uniformly dispersed oil phase in a homomixer (a stirring device consisting of high-speed rotating turbine blades and a fixed stator) (step S02) to produce a W / O emulsion (step S03). Pigment dispersions were prepared by controlling the content of each inorganic pigment: Si nanoparticles (Example), Si powder (Comparative Example 1), and titanium dioxide (Comparative Example 2) (Step S04). The pigment dispersions were prepared by ultrasonic dispersion. After uniform dispersion using ultrasound, the pigment dispersions were added to a W / O emulsion and mixed in a vortex mixer (a device used for mixing two or more liquids) (Step S05). Samples for each cosmetic product were prepared (Step S06), applied to a PET (Poly Ethylene Terephthalate) film using an applicator, and dried at room temperature for several hours.

[0050] Figure 17 shows the image of the Si nanoparticle fabrication process in step S04 described above, and Figure 18 shows the fabrication flow. As shown in the flow in Figure 18, commercially available silicon monoxide (SiO) lumps with a particle size of several millimeters were annealed under conditions higher than the melting point of silicon (step S11). The silicon nanocrystals were grown by annealing in nitrogen under conditions higher than the melting point of elemental silicon (1414°C). It is also possible to control the particle size of the silicon nanocrystals by controlling the temperature conditions during annealing. When annealing was performed at a temperature higher than the melting point of elemental silicon, a rapid increase in particle size occurred before and after exceeding the melting point, and a change in shape was observed, such as a significant improvement in circularity.

[0051] The particles obtained by annealing were etched with hydrofluoric acid (Step S12). The annealed powder (silicon dioxide particles containing silicon nanocrystals) was etched using an etching solution (a solution of nitric acid or hydrogen peroxide and hydrogen fluoride), and after etching, the etching solution was replaced with a polar solvent (such as methanol) (Step S13). Subsequently, the mixture was stirred in the polar solvent to disperse the silicon nanocrystals, and the particle size of the silicon nanocrystals in the dispersion was separated. The average particle size in the dispersion was adjusted to a particle size corresponding to the color of the target pigment, within the range of 50 nm to 200 nm (Step S14).

[0052] To standardize particle size, density gradient centrifugation or particle size sorting by adding a poor solvent is used. When using density gradient centrifugation, it is best to centrifuge the dispersion in a centrifuge tube lying horizontally to achieve high particle size resolution. By centrifugation in the horizontal direction with the centrifuge tube lying horizontally, the direction of the centrifugal force and the longitudinal direction toward the bottom of the centrifuge tube become the same, increasing the sedimentation path length and improving the resolution of density gradient centrifugation.

[0053] As shown in the schematic diagram in Figure 19, solutions in which each of the inorganic pigments Si nanoparticles (Example), Si powder (Comparative Example 1), and titanium dioxide (Comparative Example 2) were dispersed in a pigment dispersion were irradiated with light of wavelengths in the ultraviolet to visible range, and the diffuse transmittance (%) = I / I0 × 100 was measured.

[0054] Figures 20 to 22 show the spectra of diffuse transmittance (%) for wavelengths from the ultraviolet to the visible region (300 to 800 nm). Figures (1) to (5) represent the spectra of samples with a content (weight %) of 0.01, 0.05, 0.5, 2.0, and 5.0 relative to the total components of the cosmetic product. Each spectrum is plotted for four different forms: Si nanoparticles (Example), Si powder (Comparative Example 1), titanium dioxide (Comparative Example 2), and control (no pigment). The average particle sizes of the pigments used were 100 to 200 nm for Si nanoparticles (Example), 1000 nm for Si powder (Comparative Example 1), and 200 nm for titanium dioxide (Comparative Example 2). When the content was 0.01% (by weight), there was almost no difference, but when the content was 0.05% (by weight), it was found that the Si nanoparticles (example) had lower diffuse transmittance in the ultraviolet to visible range (300-800 nm) compared to other forms.

[0055] Furthermore, when the content was 0.5% (by weight) or 2.0% (by weight), the Si nanoparticles (Example) and Si powder (Comparative Example 1) had lower diffuse transmittances compared to other forms, with the Si nanoparticles (Example) having the lowest diffuse transmittance. In particular, the Si nanoparticles (Example) had a diffuse transmittance of 20% or less for wavelengths in the ultraviolet to visible range (300-600 nm). Furthermore, when the content was 5.0% by weight, the Si nanoparticles (example) had a diffuse transmittance of light in the ultraviolet to visible range (300-550 nm) of approximately 0%.

[0056] Figure 23 shows a comparison of the opacity in the visible light region of cosmetic products (foundations) in which Si nanoparticles (Example), Si powder (Comparative Example 1), and titanium dioxide (Comparative Example 2) were blended with cosmetic ingredients, resulting in pigment content (by weight) of 0.05, 0.5, 2.0, and 5.0. The cosmetic products containing each inorganic pigment were liquid foundations (film thickness 50 μm) coated and dried on the aforementioned PET film.

[0057] As shown in Figure 24, liquid foundations containing each inorganic pigment were placed on the boundary between the white and black backgrounds of the opacity test paper to check their opacity. The results showed that the liquid foundations containing Si powder (Comparative Example 1) and titanium dioxide (Comparative Example 2) showed the black background through, indicating low opacity (see (2) in the figure). In contrast, the liquid foundation containing Si nanoparticles (Example) showed the white and black backgrounds almost equally, with the black background not showing through (see (1) in the figure), confirming sufficient opacity.

[0058] Figure 25 summarizes the results of measuring the opacity of cosmetic products (foundation) in which Si nanoparticles (Example), Si powder (Comparative Example 1), and titanium dioxide (Comparative Example 2) were blended with cosmetic ingredients, resulting in pigment content (by weight) of 0.05, 0.5, 2.0, and 5.0. The measurement method involved applying the foundation to a film thickness of 50 μm on black and white opaque paper, drying it at room temperature, and then measuring the Y value of the foundation applied to the white and black areas using a colorimeter (Konica Minolta, model number: CR-20). The Y value is the visual reflectance on the Yxy chromaticity diagram in the CIE color system. Colorimeters are commonly used in the evaluation of cosmetic products, and the opacity (%) was calculated using the following formula 1.

[0059] (Math 1) Opacity (%) = (Y value of black area / Y value of white area) × 100 ... (Equation 1)

[0060] [Table 2]

[0061] In the case of Si nanoparticles (Example), a content of 0.5% or more resulted in a 100% opacity, whereas titanium dioxide (Comparative Example 2) had an opacity of only 30-45%, showing a significant difference. Furthermore, in the case of Si powder (Comparative Example 1), a content of 5.0% resulted in a 100% opacity, whereas in the case of Si nanoparticles (Example), a content of approximately one-tenth of that, 0.5%, resulted in a 100% opacity. The results above demonstrate that cosmetic products containing Si nanoparticles (example) have high opacity even in small amounts compared to others. [Examples]

[0062] (Method for producing foundation containing silicon nanocrystals) First, we will describe an example of a method for producing a UV-blocking agent for cosmetic products containing spherical silicon nanocrystals with a controlled particle size distribution. Similar to Example 2, commercially available silicon monoxide powder is used as a raw material. The silicon monoxide powder is annealed in a nitrogen (N2) atmosphere for 30 minutes, starting at a temperature lower than the melting point of elemental silicon (1414°C) and then at a temperature higher than the melting point (1425~1700°C), for example, 1450°C, to produce a silicon dioxide particle powder containing silicon nanocrystals. Next, the powder is etched using hydrofluoric acid (HF) as an etching solution to etch only the silicon dioxide portion and extract the silicon nanocrystals contained within the particles.

[0063] After etching, methanol is used as a polar solvent to replace the methanol with the etching solution. Then, the mixture is stirred with an ultrasonic homogenizer to disperse the silicon nanocrystals in methanol, and the particle size of the silicon nanocrystals is standardized using density gradient centrifugation (2000-3000G; 60 minutes) on the dispersion.

[0064] As explained in Example 2, silicon nanocrystals can also be immersed in a solution of nitric acid (HNO3) or hydrogen peroxide (H2O2) and hydrogen fluoride (HF), and etched by controlling the etching time and the concentration of nitric acid, thereby reducing and standardizing the particle size of the silicon nanocrystals and standardizing the particle size distribution in the dispersion to match the target particle size distribution.

[0065] Next, as the oil phase of the foundation, PEG-10 dimethicone, cyclopentasiloxane, and disteardimonium hectorite are blended and mixed in a weight ratio of 4:21:1. Then, as the aqueous phase of the foundation, phenoxyethanol, BG (butylene glycol), glycerin, sodium chloride, ethylenediaminetetraacetic acid (EDTA) disodium, and purified water are blended and mixed in a weight ratio of 0.5:3:2:0.5:0.05:57.95. Finally, the oil phase, aqueous phase, and a pigment dispersion liquid phase of isopropanol with added silicon nanocrystals uniformly dispersed are blended in a weight ratio of 26:64:10 to prepare the foundation. Note that the components and blending ratios of the oil and aqueous phases of the foundation are examples; other components and different blending ratios may be used, and other forms of pigment dispersions may also be used. [Industrial applicability]

[0066] This invention is useful for cosmetics such as foundations that have an ultraviolet-blocking effect, and for functional pigments that prevent resin degradation in paints.

Claims

1. A UV shielding agent containing silicon nanocrystals with a spherical shape and a peak particle size distribution within the range of 40 nm to less than 90 nm.

2. A UV shielding agent consisting of spherical silicon nanocrystals with a particle size distribution peak value in the range of 40 nm to less than 90 nm.

3. A UV shielding agent comprising a first layer containing spherical silicon nanocrystals with a peak particle size distribution between 40 nm and less than 90 nm, and a second layer containing spherical silicon nanocrystals with a peak particle size distribution between 100 nm and 220 nm.

4. A UV shielding agent containing a mixture of spherical silicon nanocrystals with a peak particle size distribution between 40 nm and less than 90 nm, and spherical silicon nanocrystals with a peak particle size distribution between 100 nm and 220 nm.

5. An ultraviolet shielding agent according to any one of claims 1 to 4, wherein the transmittance of ultraviolet light below 400 nm is 10% or less.

6. An ultraviolet shielding agent according to any one of claims 1 to 4, wherein the ultraviolet transmittance at 400 nm or less is 10% or less, the visible light transmittance at 500 nm or more is 50% or more, and the haze value at 500 nm or less is 40% or more.

7. The ultraviolet shielding agent according to claim 1 or 2, wherein the ultraviolet shielding agent is a dispersion containing the silicon nanocrystals.

8. The ultraviolet shielding agent according to claim 1 or 2, wherein the film contains the silicon nanocrystals.

9. A cosmetic product containing the ultraviolet shielding agent of claim 1 or 2, wherein the transmittance of ultraviolet light of 400 nm or less is 20% or less.

10. A cosmetic product comprising the ultraviolet shielding agent according to claim 1, characterized in that the content of the silicon nanocrystals in the ultraviolet shielding agent is 0.05% by weight or more.

11. The cosmetic product of 10, characterized in that the content is 0.2% by weight or more and 10% by weight or less.

12. The cosmetic product according to claim 10, characterized in that the aforementioned content is 0.5% by weight or more and 5% by weight or less.

13. The cosmetic product according to claim 10, characterized in that, when the film thickness of the cosmetic product is 50 μm, the diffuse transmittance in the ultraviolet region is less than 5%, and the opacity of visible light wavelengths is 50% or more.

Images