JP7748695B2 - Composite particles and cosmetics containing the same - Google Patents

Description

The present invention relates to composite particles containing base particles and microparticles attached to the surface thereof, and further to cosmetics containing the composite particles.

A technology is known in which multiple microparticles are attached to the surface of base particles that are relatively larger than the microparticles to create composite particles. Patent Document 1 discloses composite particles that use resin particles such as nylon or PMMA as the base particles and UV-blocking microparticles with an average particle size of 175 nm or less as the microparticles. Examples of UV-blocking microparticles disclosed include titanium oxide microparticles and zinc oxide microparticles. In composite particles, the base particles support the microparticles and prevent them from agglomerating. Preventing agglomeration suppresses uneven UV-blocking effects provided by the UV-blocking microparticles.

Particles used in cosmetics intended for use in contact with the skin are required to contribute to a smooth feel. Smoothness when in contact with the skin can be indicated by the mean coefficient of friction (MIU), which can be measured using a friction tester. Patent Document 2 discloses that spherical titanium oxide agglomerated particles obtained by agglomerating rod-shaped titanium oxide particles have a low MIU. According to the examples in Patent Document 2, the MIU of the spherical titanium oxide agglomerated particles is 0.26 to 0.65.

JP 2013-221148 A Japanese Patent Application Laid-Open No. 2008-56535

To the inventor's knowledge, no studies have been conducted to date on improving the smoothness of composite particles when they come into contact with the skin. Therefore, an object of the present invention is to provide composite particles with excellent smoothness.

The comparative example in Patent Document 2 also reports that the average coefficient of friction (MIU) of insufficiently aggregated, fan-shaped, i.e., non-spherical, titanium oxide agglomerated particles was 0.72. Comparing this with the examples suggests that the smoothness of composite particles would also be improved if they were spherical. In fact, the smoothness of composite particles was improved when spherical resin particles were used as the base particles of the composite particles. However, during the course of research, it was discovered that the smoothness of composite particles could also be improved by using starch particles. Because the shape of starch particles is not spherical, this effect is thought to result from the combination of starch and UV-blocking microparticles.

That is, the present invention is
The ink jet recording medium comprises a base particle and a plurality of ultraviolet-shielding fine particles attached to the base particle,
the substrate particles comprise starch;
the ultraviolet-shielding fine particles contain at least one selected from titanium oxide, zinc oxide, and cerium oxide;
Composite particles are provided.

The composite particles of the present invention can provide a smooth feel to the skin. Furthermore, because they use starch, a biodegradable material, they are also highly biodegradable. The present invention can also contribute to reducing microplastics, which have been identified as a cause of environmental pollution. Furthermore, because the aggregation of the UV-absorbing microparticles is suppressed by the base particles, they also have excellent UV-blocking properties.

1 is a scanning electron microscope (SEM) photograph of starch (corn starch) particles. 2 is a SEM photograph of composite particles obtained by combining the particles of FIG. 1 with titanium oxide fine particles. 1 is an SEM photograph of spherical nylon particles. 4 is an SEM photograph of composite particles obtained by combining the particles of FIG. 3 with titanium oxide fine particles. 1 is a SEM photograph of non-spherical nylon particles.

The following describes an embodiment of the present invention, but the following description is not intended to limit the present invention to a specific embodiment.

The composite particle of this embodiment comprises a base particle and a plurality of UV-blocking microparticles adhered to the surface of the base particle. The base particle contains starch. The UV-blocking microparticles contain at least one selected from titanium oxide, zinc oxide, and cerium oxide. The composite particle typically has a core-shell structure, with the base particle as the core and the UV-blocking microparticles as the shell. The UV-blocking microparticles are supported on the surface of the base particle, and the base particle inhibits their aggregation. In this way, changes in the apparent particle size of the UV-blocking microparticles are suppressed, and the UV-blocking effect of the UV-blocking microparticles is exerted without being inhibited by aggregation. Below, we will explain the base particle and UV-blocking microparticles that make up the composite particle, as well as a method for combining them, the properties of the resulting composite particle, and cosmetics containing the composite particle.

(Base material particles)
The base particle contains starch. The starch is, for example, at least one selected from corn starch (cornstarch), potato starch, sugarcane starch, tapioca starch, sago starch, wheat starch, and rice starch, and is preferably cornstarch. The average particle size of the base particle is not particularly limited, but may be, for example, 3 to 100 μm, preferably 5 to 60 μm, more preferably 5 to 50 μm, and in some cases, may be in the range of 5 to 20 μm, or even 5 to 18 μm. In this specification, the average particle size is defined as the particle size at 50% passage on a volume basis measured using a laser diffraction method.

Resin particles such as nylon, polystyrene, polyethylene, and PMMA have been used as base particles for composite particles. These resin particles can be easily produced by controlling their shape and surface irregularities, and can even be made into particles with extremely smooth, spherical surfaces. Spherical particles with highly smooth surfaces have a sufficiently low mean coefficient of friction (MIU), which also contributes to a lower MIU for composite particles. In contrast, starch particles have shapes such as polyhedrons and lenses and are not spherical. However, when compared as composite particles, starch particles can serve as base particles that can provide a lower MIU than spherical resin particles, which have a lower MIU.

Starch particles are a biodegradable material that decomposes quickly in nature, making them superior to petroleum-derived resin particles from an environmental perspective.

(UV shielding fine particles)
The ultraviolet-shielding microparticles contain at least one selected from titanium oxide, zinc oxide, and cerium oxide, and preferably contain titanium oxide. The ultraviolet-shielding microparticles do not need to be composed of a single type of inorganic material. For example, titanium oxide microparticles can be used as ultraviolet-absorbing microparticles without any problems even if they contain trace amounts of iron oxide and other impurities. The crystal type of titanium oxide is preferably other than the anatase type, which has high catalytic activity, specifically the rutile type. Fine particles such as titanium oxide are commercially available from Croda Japan Co., Ltd., Sakai Chemical Industry Co., Ltd., Titanium Kogyo Co., Ltd., Teika Corporation, Ishihara Sangyo Co., Ltd., etc.

The average particle size of the UV-blocking microparticles is preferably 10 to 200 nm. The lower limit of this average particle size may be 15 nm or more, and in some cases 20 nm or more. The upper limit may be 175 nm or less, and in some cases 160 nm or less. The UV-blocking properties of the UV-blocking microparticles depend on the particle size of the microparticles, and typically, the smaller the particle size, the shift in the absorption wavelength range toward shorter wavelengths. For example, to block ultraviolet B rays (UVB), UV-blocking microparticles with an average particle size of approximately 15 to 60 nm are suitable. For example, to block ultraviolet A rays (UVA), UV-blocking microparticles with an average particle size of approximately 70 to 175 nm are suitable.

(Method of compounding)
The base particles and the ultraviolet-shielding microparticles can be combined by mixing the base particles and the microparticles using a mixer such as an automatic mortar, a ball mill, a Henschel mixer, a Nauta mixer, a Loedige mixer, a V-type mixer, a hammer mill, or a pin mill.

This composite can be achieved by referring to the method described in Patent Document 1. This method includes an attachment process in which the fine particles adhere to the surface of the base particles by electrostatic forces generated between the base particles (resin particles) and the fine particles due to frictional charging between the base particles and the fine particles; and a strength enhancement process, which is performed after the attachment process, in which the base particles with the fine particles attached collide with each other to increase the adhesion strength of the fine particles to the base particles. The attachment process utilizes the phenomenon in which different substances become charged according to a triboelectric series when they come into contact and separate. Base particles and fine particles repel each other because they have the same charge due to charging, while base particles and fine particles, which have different charges, attract each other. This electrostatic attraction results in the fine particles being densely supported on the surface of the base particles. In the strength enhancement process, the impact force associated with the collision improves the adhesion strength between the base particles and the fine particles. By performing the above-mentioned attachment and strength enhancement processes, it is possible to produce composite particles with improved adhesion strength of UV-irradiated fine particles compared to conventional methods.

Details of this preferred method are described in Patent Document 1. That is, the above-mentioned adhesion process and preferred strength-enhancing process can be carried out using, for example, a Henschel mixer. Specifically, the adhesion process is carried out by adding base particles and fine particles to a Henschel mixer and rotating the agitator blades at a first speed for a predetermined time to mix the base particles and fine particles. Subsequently, the strength-enhancing process is carried out by rotating the agitator blades of the Henschel mixer at a second speed, which is faster than the first speed, for a predetermined time. The strength-enhancing process is carried out by adding only base particles with UV-absorbing fine particles attached to them, as particles whose surfaces are composed of inorganic or metal, to the Henschel mixer. The "predetermined time" mentioned above varies depending on factors such as the amount of particles added. For the adhesion process, for example, it is 1 minute or more, particularly 2 to 10 minutes. Even if it is 10 minutes or more, the adhesion state is good, but long production times decrease cost-effectiveness. For the strength-enhancing process, for example, it is 15 minutes or more, particularly 20 to 60 minutes. Even if it is 60 minutes or more, strength improvement is still effective, but long production times decrease cost-effectiveness.

As the processing time progresses, compounding progresses, and the fine particles penetrate between the agglomerated starch particles, breaking up the agglomerations and bombarding the surface of the starch particles with the fine particles, promoting compounding.

The above-described method allows the ultraviolet-shielding microparticles to adhere to the base particles without relying on the adhesive strength of other materials. Therefore, the adhesion state between the ultraviolet-shielding microparticles and the base particles is maintained even in the absence of an organic material such as wax that encapsulates and integrates the ultraviolet-shielding microparticles and the base particles. In this embodiment, the composite particles do not need to contain an organic material that coats both the base particles and the ultraviolet-shielding microparticles and integrates them.

The mass ratio of the ultraviolet-absorbing microparticles to the total amount of the base particles and ultraviolet-absorbing microparticles is not particularly limited, but is preferably 50% or more, more preferably 55% or more, particularly 60% or more, and especially 65% or more.

(Characteristics of composite particles)
The mean coefficient of friction (MIU) of the composite particles of this embodiment can be reduced to 0.23 or less, and even 0.22 or less. However, the MIU value differs depending on the type of ultraviolet-shielding microparticles, the ratio of base particles to microparticles, etc., and therefore the MIU of the composite particles of this embodiment is not limited to the above. The composite particles of this embodiment can have a lower MIU than those using conventional resin particles, provided that the type of microparticles, etc., is the same.

(Cosmetics)
The composite particles of this embodiment are suitable for incorporation into cosmetics. Cosmetics containing the composite particles of this embodiment are not particularly limited in type, but include facial cosmetics, makeup cosmetics, and the like. In particular, for facial cosmetics such as foundations and face powders, there is a particularly high demand for materials that block ultraviolet rays. The form of the cosmetics is not particularly limited, but may be powder, cake, pencil, stick, ointment, liquid, emulsion, cream, or the like.

The present invention will be further explained below with reference to examples, but the present invention is not limited to the following.

[Composite particles]
Example 1
Cornstarch White (see FIG. 1; average particle size 15 μm) manufactured by Nippon Corn Starch Co., Ltd. was used as the starch particles, and MT100TV (average particle size 15 nm) manufactured by Teika Corporation was used as the titanium oxide fine particles.

40 parts by mass of starch particles and 60 parts by mass of titanium oxide microparticles were added to a Henschel mixer and mixed for 3 minutes at a peripheral speed of 40 m/s. The apparent specific volume of the processed product was 1.6 mL/g. Processing was then continued for 20 minutes at a peripheral speed of 100 m/s to obtain composite particles (see Figure 2).

(Comparative Example 1)
Composite particles were obtained in the same manner as in Example 1, except that spherical nylon particles SP10 (see FIG. 3; average particle size 10 μm) manufactured by Toray Industries, Inc. were used instead of the starch particles (see FIG. 4).

The average coefficient of friction (MIU) was measured for each of the composite particles obtained above and each of the base particles used using them using a friction feel tester KES-SE manufactured by Kato Tech Co., Ltd. Silicone was used as the friction probe, the load was 25 g, and the measurement speed was 1 mm/sec. The measurement object was an artificial leather manufactured by Idemitsu Technofine Co., Ltd., where 5 mg of the base particles or composite particles was evenly spread over a 24 cm ² (8 x 3 cm) area of Saplarre (registered trademark; artificial leather). The results obtained are shown in Table 1.

By compounding, the MIU of the starch particles was reduced to below that of spherical nylon particles. Among resin particles, SP10 has a particularly low MIU due to its spherical shape. For example, the MIU of non-spherical nylon particles (see Figure 5; Orgasol (registered trademark) Green Touch manufactured by Arkema) was measured and found to be 0.491. Even when composite particles are produced using such resin particles as base particles, the MIU value of the composite particles does not fall below the minimum value of 0.26 obtained by agglomeration of titanium oxide microparticles (see Patent Document 2).

[Cosmetics]
(Examples 2-3/Comparative Examples 2-3)
A sunscreen was prepared according to the formulation shown in Table 2. Specifically, components 1 to 9 (oil phase) and components 10 to 13 (aqueous phase) were mixed by stirring, and then the aqueous phase was added to the oil phase to emulsify. The composite particles were prepared in the same manner as in Example 1, except that "Solabail XTP-1" manufactured by Croda Japan Co., Ltd. was used instead of MT100TV as the titanium oxide microparticles. A powder foundation was also prepared according to the formulation shown in Table 3. Specifically, components 1 to 7 were mixed and pulverized and transferred to a high-speed blender, to which a mixture of components 8 to 12 was added, mixed, and pulverized. The resulting mixture was then press-molded into a medium-sized container.

The SPF measurement results are shown in Table 4. Evaluation items for cosmetic feel, such as spreadability, roughness, squeaky feeling, and fit (adhesion), were each evaluated by 10 expert panelists, and the scores of each panelist were totaled based on the following evaluation criteria. The results are shown in Table 5.
・Evaluation criteria 5 points: very good 4 points: good 3 points: average 2 points: poor 1 point: very poor ・Evaluation criteria ◎: The total score is 40 points or more.
○: The total score is 20 points or more and less than 30 points.
△: The total score is 10 points or more but less than 20 points.
×: The total score is less than 10 points.

Claims (6)

The ink jet recording medium comprises a base particle and a plurality of ultraviolet-shielding fine particles attached to the base particle,
the base particle has a core-shell structure in which the core is made of the base particle and the ultraviolet-shielding fine particles are made of the shell,
the substrate particles comprise starch;
the ultraviolet-shielding fine particles contain at least one selected from titanium oxide, zinc oxide, and cerium oxide;
composite particles.
However, this does not include composite particles in which, when the shell is a first coating layer, the first coating layer is at least partially covered with a second coating layer containing a hydrophobic block copolymer. The ink jet recording medium comprises a base particle and a plurality of ultraviolet-shielding fine particles attached to the base particle,
the substrate particles comprise starch;
the ultraviolet-shielding fine particles contain at least one selected from titanium oxide, zinc oxide, and cerium oxide,
The average coefficient of friction (MIU) is 0.23 or less.
composite particles. The ink jet recording medium comprises a base particle and a plurality of ultraviolet-shielding fine particles attached to the base particle,
the substrate particles comprise starch;
the ultraviolet-shielding fine particles are titanium oxide fine particles,
the mass ratio of the ultraviolet-shielding microparticles to the total amount of the base particle and the ultraviolet-shielding microparticles is 50% or more;
composite particles.
However, this does not include composite particles in which, when the layer of the plurality of ultraviolet fine particles is a first coating layer, the first coating layer is at least partially covered with a second coating layer containing a hydrophobic block copolymer. The composite particle according to claim 1 or 2, wherein the mass ratio of the ultraviolet-shielding microparticles to the total amount of the base particle and the ultraviolet-shielding microparticles is 50% or more. The composite particles described in claim 1 or 3 have an average coefficient of friction (MIU) of 0.23 or less. A cosmetic comprising the composite particles described in any one of claims 1 to 5.