Methods and products for producing metal oxide pigment composites with controlled aggregation properties

Abstract

A process for the preparation of a composite comprising submicron-sized particles of a metal oxide pigment and a natural-based organic compound is disclosed, the process comprising ball milling the metal oxide pigment and an oligomeric and / or polymeric carbohydrate together to obtain a pigment composite comprising particles having a submicron particle size distribution and an outer surface covered with the oligomeric and / or polymeric carbohydrate. Also disclosed is the pigment composite thus obtained comprising pigment particles having an average hydrodynamic diameter of less than 1 μm.

Description

[Technical Field]

[0001] The present invention relates to the field of pigments and the formulation of cosmetics and coatings containing them, in particular to aqueous-based pigment compositions of submicron particle size distribution and dispersions thereof. [Background technology]

[0002] In some industrial applications, particularly in the cosmetics field, pigments generally need to have a size between 0.3 μm and 0.8 μm.

[0003] Commercially available pigments have particle sizes closer to the micrometer scale than the nanometer scale, making it difficult to obtain a uniform dispersion and therefore difficult to ensure uniform coverage of the surface to which the pigmented formulation is applied.

[0004] The particle size of commercially available pigments can be from 0.1 μm to even 10 μm.

[0005] Various milling techniques can be used to produce formulations that are homogeneous throughout their shelf life and possibly evenly coat various types of surfaces.

[0006] Reducing the particle size to the submicron scale not only improves the stability of the formulations in which the pigments are dispersed, but also improves the overall quality of such formulations during application, for example by reducing the unwanted striping phenomenon.

[0007] Size reduction by milling is well known and is a readily engineered method that is applied not only in the production of metals but also as a post-production treatment of a variety of solids.

[0008] By varying the milling parameters, the particle size that is reduced during the milling process can be controlled.

[0009] However, pigment particles, when dispersed in certain suspensions or formulations, tend to fuse together on contact to form larger particles, resulting in the phenomena of settling, creaming, flocculation and / or coalescence that determine the separation of suspensions and formulations.

[0010] Specifically, most commonly used metal oxide-based pigments form stable compositions in neutral to slightly basic environments, but the colloidal properties of the resulting micro- and nanostructures exhibit significant instability as the pH of the dispersion medium increases. The pH-dependent acceleration of the aggregation and destabilization of iron oxide nanoparticles has been disclosed in Non-Patent Document 1.

[0011] Wetting and dispersing additives are used to improve the physicochemical and colloidal properties.

[0012] The use of artificial surfactants as wetting and dispersing additives is known in the art.

[0013] Surfactants can interact in a variety of ways, among which non-bonded interactions usually predominate. Among these interaction forces, electrostatic properties have traditionally been considered the most important stabilizing factor. In water-based dispersions, concentrated pigment particles are surrounded by an electrochemical double layer of oppositely charged ions or dipoles that are intimately attached to the pigment.

[0014] The strength of the attractive and repulsive forces is distance dependent, and in a strong, pronounced double layer, the repulsion coefficient dominates. Thus, surfactants can be successful in obtaining stable dispersions containing pigments.

[0015] However, if the electrochemical double layer is damaged, for example by the addition of an electrolyte, the attractive forces become dominant and the dispersion collapses, as may occur, for example, during the preparation of cosmetic formulations.

[0016] Another common problem associated with surfactants and other additives is that they can cause significant drawbacks in the properties of the formulations to which they are added. Rheological changes, such as viscosity loss, are quite common. Furthermore, the use of surfactants significantly affects a wide range of essential properties of the formulation, such as color strength, hiding power, flocculation, gloss, flooding, and floating.

[0017] Therefore, there is a great need to provide new technologies for producing stable formulations containing pigments, especially in the field of cosmetics and coatings.Such stable formulations containing pigments are expected to guarantee at least the following properties: i) minimal complexity of the production process, ii) good properties in terms of dispersibility, iii) good stability of the latter, and iv) strong coloring hue. [Prior art documents] [Non-patent literature]

[0018] [Non-Patent Document 1] Schudel et al., J. Colloid Interface Sci., 1997, 196, 241 Summary of the Invention

[0019] The present invention relates to a process for the manufacture of a pigment composite comprising pigment particles having a submicron size. Specifically, the main object of the present invention is a process for the preparation of a composite comprising submicron-sized particles of a metal oxide pigment and a natural-based organic compound, the process comprising the step of ball milling together a metal oxide pigment and an oligomeric and / or polymeric carbohydrate to obtain a pigment composite comprising particles having a submicron particle size distribution and an outer surface covered with an oligomeric and / or polymeric carbohydrate.

[0020] According to a preferred embodiment, said pigment is a transition metal oxide pigment.

[0021] According to another aspect, the invention also provides novel pigment complexes obtainable by the process described above.

[0022] It has been experimentally observed that the novel pigment composites described above contain particles with a smaller hydrodynamic diameter at neutral, slightly basic and weakly basic pH than the hydrodynamic diameter of the same type of pigment particles that have not undergone the preparation process according to the present invention. [Brief explanation of the drawings]

[0023] [Figure 1] 1 shows a skin preparation obtained by using a mixture of metal oxide pigment complexes according to the present invention. [Figure 2] The pigment composites obtained in Examples 1 to 3 below are shown dispersed in water. [Figure 3] 2 shows the dispersion shown in FIG. 2 once the supernatant has been removed (remaining dispersion: left vial; supernatant: right vial). [Figure 4] An example of a roll ball mill is shown. [Figure 5] An example of a cylindrical ball mill is shown. DETAILED DESCRIPTION OF THE INVENTION

[0024] According to the present invention, the term "pigment" means a colored, white, or black substance that is capable of permanently imparting its own color or hue to a dispersed material or substance and of imparting a specific color to reflected or transmitted light as a result of selective absorption of specific wavelengths, and pigments usually have a high coloring strength relative to the material or substance with which they are mixed to color it.

[0025] According to the present invention, the term "particle size distribution" means a numerical range including a minimum and a maximum value of the diameter of the particles forming the complex according to the present invention.

[0026] According to the present invention, the expression "submicron size" means a size of less than 1 μm. MedianBy "particles" is meant particles having a diameter of 1 / 2 mm.

[0027] The term "ball mill" as used herein broadly refers to any milling apparatus comprising a grinding chamber (e.g., a jar) into which the material to be milled can be introduced, the grinding chamber containing one or more freely moving balls, the movement of which causes the grinding of the material to be milled; as a general, non-limiting rule, the movement of the balls can be obtained by applying (one or more) rotational, gyrating, and / or vibrating motions to said grinding chamber.

[0028] One preferred example of a ball mill is a "planetary ball mill," in which the grinding chamber can be set to rotate about its vertical axis, and optionally a complementary orbital motion about a suitable center of rotation is further applied to the grinding chamber, such motion(s) causing the grinding balls in the grinding chamber to move freely and mix with the material to be ground, causing its grinding. An example of a commercially available planetary ball mill is the Retsch PM 100 device.

[0029] Further examples of ball mills are the roll ball mill and the cylindrical ball mill. In both cases, the grinding chamber is set to rotate about its horizontal axis, and this movement causes the grinding balls in the grinding chamber to move freely, mix with the material to be milled, and grind it. In a roll ball mill, the rotational motion is applied to the grinding chamber by contact of its outer surface with counter-rotating rotating guides or rolls (Figure 4). An example of a commercially available roll ball mill is the Tencan GQM-2-5. In a cylindrical ball mill, the rotational motion is applied to an element that extends from the horizontal axis of the grinding chamber or is indirectly fixed in rotation by a gear / V-belt (Figure 5). An example of a commercially available cylindrical ball mill is the Tencan QM-30L.

[0030] According to the present invention, the expression "ball to mass ratio" intends the ratio between the total weight of balls / beads contained in the ball mill used during said grinding step b) and the total mass of the materials to be ground, i.e. the metal oxide pigments and natural-based organic compounds fed to the ball mill, or other materials finally fed to the ball mill, e.g. before or during grinding step b).

[0031] According to the present invention, the term "shelf life" intends the length of time that the pigment complex obtained by the process of the present invention can be stored at room temperature without becoming unsuitable for use, i.e., obtaining a stable formulation with respect to its phase separation and color when properly dispersed in a medium, in particular an aqueous medium.

[0032] The process of the present invention for the preparation of a composite comprising submicron-sized particles of a metal oxide pigment and a natural-based organic compound comprises: a) providing a metal oxide pigment and an oligomeric and / or polymeric carbohydrate; b) milling said metal oxide pigment and said oligomeric and / or polymeric carbohydrate in a ball mill to obtain a pigment composite comprising metal oxide particles having a submicron particle size distribution and an outer surface partially or completely covered by said oligomeric and / or polymeric carbohydrate, The mass ratio between said metal oxide pigment and said oligomeric and / or polymeric carbohydrate provided in said step a) is comprised between 1:10 and 10:1.

[0033] Preferably, the grinding step b) is carried out under dry milling conditions.

[0034] According to a preferred embodiment, the mass ratio between said pigment and said oligomeric and / or polymeric carbohydrate is comprised between 1:5 and 5:1.

[0035] Advantageously, as shown in the experimental part, the particle size distribution of the pigment complexes obtained by the process according to the invention can be reduced when the mass ratio between the pigment and the oligomeric and / or polymeric carbohydrate is increased.

[0036] Preferably, the grinding step b) is carried out with a ball-to-mass ratio generally comprised between 2:1 and 15:1, with ball-to-mass ratios particularly suitable for planetary ball mills more preferably comprised between 3:1 and 10:1, and ball-to-mass ratios particularly suitable for roll or cylindrical ball mills more preferably comprised between 2:1 and 7:1.

[0037] Advantageously, as shown in the experimental part, when the ball-to-mass ratio is reduced, the particle size distribution of the pigment complex obtained by the process according to the invention can also be reduced.

[0038] Alternatively, the grinding step b) is carried out under wet milling conditions.

[0039] When the process of the present invention is carried out under wet milling conditions, a wetting material or lubricant can be added to the metal oxide pigment and oligomeric and / or polymeric carbohydrate before or during the grinding step b).

[0040] Preferably, the wetting material is water, ethyl alcohol or a surfactant.

[0041] More preferably, the surfactant is selected from the group comprising esters of long chain fatty acids, aryloxy alcohols, polymeric alcohols, alkyl ethers of glycerol, and the like.

[0042] Even more preferably, the surfactant is added in an amount comprised between 0.5% and 2.5% by weight of the total weight of material fed to the ball mill.

[0043] Generally speaking, the grinding step b) is preferably carried out at a rotation speed between 200 rpm and 700 rpm, more preferably between 300 rpm and 550 rpm, for a time between 0.5 and 15 hours, more preferably between 1 and 9 hours, these conditions being particularly suitable for a planetary ball mill.

[0044] Alternatively, the grinding step b) is preferably carried out at a rotation speed between 20 rpm and 400 rpm, more preferably between 20 rpm and 200 rpm, for a time between 0.5 hours and 15 hours, more preferably between 1 hour and 9 hours, these conditions being particularly suitable for a roll ball mill or a cylindrical ball mill.

[0045] In all the above-mentioned embodiments, preferred, non-limiting examples of materials for the grinding balls include zirconia (i.e., zirconium oxide), stainless steel, etc. Preferred, non-limiting examples of materials for the grinding chamber include zirconia, perfluorinated polymers, stainless steel, etc. Preferred, non-limiting combinations of materials for the grinding balls and grinding chamber include alumina or zirconia balls in a ceramic chamber, zirconia balls in a zirconia chamber, zirconia balls in a polymeric perfluorinated chamber, and stainless steel balls in a stainless steel chamber. In addition to the above-mentioned examples, the above-mentioned materials for construction, as well as the dimensions of the grinding chamber and the dimensions / weight / amount of the grinding balls, can be selected according to options customarily applied in the art and can possibly be further adapted depending on the type and amount of material to be milled.

[0046] As an advantage, the process of the invention makes it possible to obtain a pigment complex that does not undergo reagglomeration of the particles during the milling process and that is stable with respect to its color during its shelf life.

[0047] In particular, as will be shown in detail with reference to the experimental part, such pigment complexes can be easily and stably dispersed in liquid media, especially aqueous media, to give suspensions with good stability and strong color hues.

[0048] During the aforementioned grinding step b), the movement of the pigment particles is restricted and the chemically preferred arrangement of interacting atoms is restricted by the outer surface of the particles, which are formed to have a reduced average size when compared to the average size of natural metal oxide pigments.

[0049] The newly formed surface can be readily coated with the latter material(s) by co-grinding oligomeric and / or polymeric carbohydrate materials to reduce re-agglomeration. In particular, the hollow polymeric structures of cyclodextrins or fibrous or lamellar polysaccharides such as ionic and nonionic cellulose and cellulose derivatives readily incorporate pigment particles.

[0050] Such coated association particle complexes have a hydrophilic outer surface that plays an important role in the colloidal stability of formulations in which they are dispersed.

[0051] A further advantage is that during the grinding step b) oxo-complexes and / or hydrogen-bond stabilized associations are formed between the metal oxide pigments and the oligomeric and / or polymeric carbohydrates, which prevent the formation of large particles under mechanochemical conditions, i.e., during the grinding step b), but also especially when the pigment complexes thus obtained are dispersed in a suitable aqueous medium.

[0052] In particular, as will be shown in detail in the experimental part, the aforementioned pigment complexes can be easily dispersed in aqueous media having a neutral to basic pH.

[0053] As a further improvement, the stable formulation so formed, when dispersed in aqueous media, has favorable sedimentation properties that remain even after pH shifts or adjustments.

[0054] A further improvement achieved by the process according to the invention is the increased color stability of the pigment complexes thus obtained, depending on their particle size, in color and shade: the limited self-aggregation of submicrometer and nanometer sized particles preserves the optical properties of the pigments, and their color can remain intact for a long time in dispersed and undispersed forms.

[0055] Furthermore, as will be disclosed in more detail in the experimental part, a further improvement of the present invention is that the particles of the pigment complex obtained by the aforementioned process do not adhere to the surfaces of packaging materials such as glass and plastics and do not cause unwanted coloration of those materials.

[0056] According to the process of the present invention, the neutral-based organic compounds, i.e., oligomeric and / or polymeric carbohydrates, can be added and mixed with the aforementioned metal oxide pigments at any stage of the process, preferably before or during the grinding step b).

[0057] Preferably, the metal oxide pigment is a transition metal oxide pigment.

[0058] More preferably, the metal oxide pigment may be selected from the group consisting of iron(III) oxide (CAS No. 1309-37-1 (red pigment) or CAS No. 51274-00-1 (yellow pigment)), iron(III) oxide (CAS No. 1317-61-9, black pigment), titanium oxide (CAS No. 13463-67-7), chromium(III) oxide (CAS No. 1308-38-9), manganese(IV) oxide (CAS No. 1313-13-9), zinc oxide (CAS No. 1314-13-2), cobalt(II) oxide (CAS No. 1307-96-6), zirconium(IV) oxide (CAS No. 1314-23-4), tungsten(VI) oxide (CAS No. 1314-35-8), and any combination thereof.

[0059] Preferably, the oligomeric and / or polymeric carbohydrate is selected from the group consisting of ionic cellulose, non-ionic cellulose, ionic or non-ionic cellulose derivatives, starch, alginate, hyaluronate, chitosan, carrageenan, pectin, cyclodextrin, and any combination thereof.

[0060] In a further preferred form, the oligomeric and / or polymeric carbohydrate is a cyclodextrin, more preferably a β-cyclodextrin.

[0061] In an equally preferred form, the oligomeric and / or polymeric carbohydrate is an ionic cellulose, a non-ionic cellulose or a cellulose derivative, more preferably carboxymethylcellulose or a salt thereof.

[0062] According to a preferred embodiment of the present invention, a base additive is added to the metal oxide pigment and the oligomeric and / or polymeric carbohydrate.

[0063] According to the process of the present invention, the base additive can be added and mixed with the metal oxide pigment at any stage of the process, preferably before or during the milling step b).

[0064] The inorganic base additive can be an inorganic or organic base according to the Bronsted-Lowry acid base theory.

[0065] In an equally preferred form, the base additive can be an inorganic base additive, and preferably, the inorganic base additive is selected from the group consisting of alkali hydroxides, alkaline earth hydroxides, carbonates, bicarbonates, and any combination thereof.

[0066] More preferably, the inorganic base additive is sodium hydroxide, sodium carbonate or sodium bicarbonate.

[0067] Preferably, the weight ratio between the pigment and the inorganic base additive is comprised between 1:2 and 10:1.

[0068] More preferably, the weight ratio between the pigment and the inorganic base additive is comprised between 1:2 and 5:1.

[0069] According to a preferred embodiment of the present invention, the base additive is an organic base additive, and preferably, the organic base additive is selected from an amino acid, an alkyl or aryl alkyl amine, a hydroxyalkyl or (hydroxy)aryl alkyl amine, a hydroxyalkyl or (hydroxy)aryl alkyl urea, a hydroxyalkyl or (hydroxy)aryl alkyl thiourea, or any combination thereof.

[0070] The amino acids can be L-amino acids, D-amino acids, or mixtures thereof.

[0071] Preferably, the organic base additive is arginine, tris(hydroxymethyl)methylamine or urea.

[0072] According to a further preferred embodiment, the base additive is a combination of an inorganic base and an organic base, preferably a combination of any one of the aforementioned inorganic base additives with any one of the aforementioned organic base additives.

[0073] Advantageously, the addition of a base additive to the metal oxide pigment and the oligomeric and / or polymeric carbohydrate can improve the ability of the pigment complex to form a stable formulation under moderately basic pH conditions and after pH shifts or adjustments.

[0074] More particularly, it has been surprisingly discovered that the addition of the above-mentioned base additives allows some classes of oligomeric and / or polymeric carbohydrates to adhere better to the pigment particles under formation during the aforementioned milling step b).

[0075] For example, as shown in the experimental section below, when natural metal oxide pigments are milled with cyclodextrin and a base additive, the resulting pigment complex can be better dispersed in an aqueous-based dispersion compared to a similar pigment complex produced without the addition of a base additive.

[0076] Without being bound by scientific theory, it is believed that when natural metal oxide pigments are milled with cyclodextrin and a base additive, the base additive deprotonates some of the hydroxyl groups of the cyclodextrin, forming strong intermolecular interactions with the surface of the forming pigment particle, thereby enhancing the ability of the cyclodextrin to be described below.

[0077] According to a preferred embodiment of the process, during step a) of providing a metal oxide pigment and an oligomeric and / or polymeric carbohydrate, the oligomeric and / or polymeric carbohydrate provided is β-cyclodextrin, and at the same time, the inorganic base additive added to the metal oxide pigment and the β-cyclodextrin is NaOH.

[0078] According to another preferred embodiment of the process, during step a) of providing a metal oxide pigment and an oligomeric and / or polymeric carbohydrate, the oligomeric and / or polymeric carbohydrate provided is β-cyclodextrin, and at the same time, the inorganic base additive added to the metal oxide pigment and the β-cyclodextrin is NaHCO3.

[0079] According to another preferred embodiment of the process, during step a) of providing a metal oxide pigment and an oligomeric and / or polymeric carbohydrate, the oligomeric and / or polymeric carbohydrate provided is β-cyclodextrin, and at the same time, the organic base additive added to the metal oxide pigment and the β-cyclodextrin is arginine.

[0080] According to another preferred embodiment of the process, during step a) of providing a metal oxide pigment and an oligomeric and / or polymeric carbohydrate, the oligomeric and / or polymeric carbohydrate provided is β-cyclodextrin, and at the same time, the organic base additive added to the metal oxide pigment and the β-cyclodextrin is tris(hydroxymethyl)methylamine.

[0081] According to another preferred embodiment of the process, during step a) of providing a metal oxide pigment and an oligomeric and / or polymeric carbohydrate, the oligomeric and / or polymeric carbohydrate provided is β-cyclodextrin, and at the same time, the organic base additive added to the metal oxide pigment and the β-cyclodextrin is urea.

[0082] According to an embodiment of the process, auxiliary materials may be milled together with the metal oxide pigment and the oligomeric and / or polymeric carbohydrate during the milling step b).

[0083] According to the process of the present invention, the auxiliary materials can be added and mixed with the aforementioned natural metal oxide pigments at any stage of the process, preferably before or during the grinding step b).

[0084] More preferably, said auxiliary material may be selected from the group comprising bactericides, stabilizers or fillers, or hydrotropic active additives, such as urea or other organic or inorganic salts.

[0085] According to another aspect, the present invention also relates to a pigment composite obtainable by the process described above.

[0086] As shown in the experimental part below, the pigment complexes according to the invention comprise pigment particles having a submicron particle size distribution and an outer surface partially or completely covered by the above oligomeric and / or polymeric carbohydrates.

[0087] More particularly, the particles of the complexes of the invention, when dispersed in an aqueous medium, have an average hydrodynamic diameter of less than 1 μm, preferably between 50 nm and 800 nm, more preferably between 100 nm and 500 nm, measured by dynamic light scattering (also called photon correlation spectroscopy or quasi-elastic light scattering) according to procedure ISO 22412:2017.

[0088] According to the present invention, particle sizes and their distributions are appropriately characterized by the hydrodynamic diameter of the particles measured by photon correlation spectroscopy, also known as dynamic light scattering (DLS) (Chu, B. Laser light scattering: Basic Principles and Practice. Academic Press, 1992; Berne, BJ; Pecora, R. Dynamic Light Scattering. Courier Dover Publications, 2000). The effective hydrodynamic diameter of the particles is calculated by multimodal analysis of the measured autocorrelation function of the scattered light, as taught by Frisken B. et al. (J. Applied Optics, 2001, 40, 4087-4091).

[0089] According to a preferred embodiment, the aforementioned pigment complex can be stably suspended in an aqueous medium, the aqueous medium preferably having a pH comprised between 6 and 12, more preferably between 6 and 9.

[0090] More preferably, the pigment complex according to the present invention has a shelf life comprised between 6 and 48 months.

[0091] As already explained with respect to the present process and shown in detail in the experimental part, the pigment complex of the present invention does not undergo particle reagglomeration during the milling process and is absolutely stable with respect to its color during its shelf life.

[0092] In particular, as will be shown in detail with reference to the experimental part, such pigment complexes can be easily and stably dispersed in liquid media, especially aqueous media, to give suspensions with good stability and strong color hues.

[0093] When the grinding step b) is carried out under dry milling conditions, the pigment complex is in dry form. When the grinding step b) is carried out under wet milling conditions, the pigment complex of the present invention can be in the form of a viscous paste, for example, an aqueous paste.

[0094] Consistently, according to another aspect, the present invention also relates to the use of the aforementioned pigment complex for coloring cosmetics, paints, coating formulations or other applications where a smooth, evenly covered and colored surface is required.

[0095] The use of the aforementioned pigment complexes in cosmetics is particularly preferred.

[0096] According to a preferred embodiment, the pigment complex of the present invention can be effectively used for preparing a cosmetic composition, more preferably for coloring a cosmetic composition, such as a foundation, a primer, a concealer, a lipstick, a lip gloss, a bronzer, an eye shadow, an eye liner, an eyebrow, a mascara, an enamel, or any other cosmetic composition containing a pigment. This embodiment also extends to a method for preparing, in particular for coloring, a cosmetic composition, such as a foundation, a primer, a concealer, a lipstick, a lip gloss, a bronzer, an eye shadow, an eye liner, an eyebrow, a mascara, an enamel, or any other cosmetic composition, said method comprising the step of adding the pigment complex of the present invention to the respective cosmetic composition.

[0097] Therefore, in another aspect, the present invention relates to a cosmetic composition comprising the pigment complex described above, said cosmetic composition being preferably a facial cosmetic product.

[0098] Alternatively, the aforementioned pigment complexes can be used as coloring additives in preparations for coloring cement, gypsum plaster, soap, paper, aqueous and non-aqueous printing inks, such as inks for gravure printing, screen printing or paper printing, rubber gratings or leather coatings. This embodiment also extends to a method for coloring materials such as cement, gypsum plaster, soap, paper, aqueous and non-aqueous printing inks, said method comprising the step of adding the pigment complex of the present invention to the respective composition of these.

[0099] The invention will now be illustrated, but not limited to, by the following examples.

[0100] experiment Example 1: Preparation of pigment complex under neutral conditions β-Cyclodextrin was added to the natural metal oxide according to a mass ratio of metal oxide / carbohydrate equal to 1: 2. Red iron oxide supplied by Sun Chemical Co. was used.

[0101] The β-cyclodextrin and the natural metal oxide were mixed together and milled in a planetary ball mill (Retsch PM 100) at 500 rpm according to a ball to mass ratio equal to 12: 1. The milling process was carried out for 90 minutes.

[0102] A fine red powder was obtained.

[0103] The procedure was repeated using carboxymethylcellulose (CMC) instead of β-cyclodextrin (β-CD), keeping the metal oxide / carbohydrate ratio equal to 1:2, and the milling process was carried out under the same conditions.

[0104] A fine red powder was obtained.

[0105] Both the β-cyclodextrin and carboxymethylcellulose procedures were then repeated for three other natural pigments at equal metal oxide / carbohydrate ratios and under the same milling conditions. The natural pigments used were as follows: yellow iron oxide, white titanium oxide, and green chromium oxide (all metal oxides supplied by Sun Chemical Co.).

[0106] The total number of experiments under neutral conditions was eight.

[0107] Example 2: Preparation of pigment complex under slightly basic conditions β-Cyclodextrin was added to the natural metal oxide according to a ratio of metal oxide / carbohydrate equal to 1:2. Red iron oxide supplied by Sun Chemical Company was used.

[0108] β-cyclodextrin and natural metal oxide were mixed together and sodium bicarbonate was added to them, and the mass ratio between metal oxide, β-cyclodextrin and sodium bicarbonate was 1:2:1, respectively.

[0109] The mixture thus obtained was added to a planetary ball mill (Retsch PM 100) and then milled at 500 rpm according to a ball to mass ratio equal to 12: 1. The milling process was carried out for 90 minutes.

[0110] A fine red powder was obtained.

[0111] The procedure was repeated with equal metal oxide / carbohydrate / NaHCO3 ratios and under the same milling conditions for three other natural pigments: yellow iron oxide, white titanium oxide, and green chromium oxide.

[0112] The total number of experiments under slightly basic conditions was four.

[0113] Example 3: Preparation of pigment complex under basic conditions β-Cyclodextrin was added to the natural metal oxide according to a mass ratio of metal oxide / carbohydrate equal to 1: 2. Red iron oxide supplied by Sun Chemical Company was used.

[0114] β-cyclodextrin and natural metal oxide were mixed together and sodium hydroxide was added to them, and the mass ratio between metal oxide, β-cyclodextrin and sodium hydroxide was 2:4:1, respectively.

[0115] The mixture thus obtained was added to a planetary ball mill (Retsch PM 100) and then milled at 500 rpm using a ball to mass ratio equal to 12: 1. The milling process was carried out for 90 minutes.

[0116] A fine red powder was obtained.

[0117] The procedure was repeated for three other natural pigments under the same milling conditions with metal oxide / carbohydrate / NaOH ratios; the natural pigments used were as follows: yellow iron oxide, white titanium oxide, and green chromium oxide.

[0118] The total number of experiments under basic conditions was four.

[0119] Example 4: Milling of natural pigments under neutral conditions (comparative) The procedure of Example 1 was carried out under the same milling conditions using only natural red iron oxide, resulting in a red, milled pigment in powder form.

[0120] The powder thus obtained exhibited a slightly darker color when compared with the pigment complex according to the invention obtained in Example 1.

[0121] The above procedure was also carried out on natural yellow iron oxide, natural white titanium oxide, and green chromium oxide.

[0122] Example 5: Determination of Hydrodynamic Diameter in Neutral Suspension To assess the particle size and its distribution, the pigment complex obtained in Example 1 was suitably characterized by photon correlation spectroscopy.

[0123] 1-5 mg of each sample prepared in Example 1 was suspended in 4 ml of distilled water in a clear plastic cuvette (90° scattering of 678 nm laser light) and light scattering was measured with a Brookhaven 90Plus Particle Size Analyzer instrument according to procedure ISO 22412:2017.

[0124] The samples were freshly shaken and particle size was calculated from a multimodal intensity distribution model by weighted averaging of nine consecutive experiments (data collection period: 30 s for each run).

[0125] Table 1 below shows the calculated hydrodynamic diameter (nanometer) distribution of pigment complexes in neutral suspension (pH=6-7).

[0126] The pigment powder obtained in Example 4 was also successfully characterized by photon correlation spectroscopy.

[0127] Table 1 shows the calculated hydrodynamic diameter distribution of the milled pigment powders obtained in Examples 1 and 4 in neutral suspension (pH=6-7).

[0128] [Table 1]

[0129] It is clear that the red iron oxide particles obtained by the process according to the invention generally have smaller hydrodynamic diameters. The distribution of hydrodynamic diameters is significantly shifted to 150-200 nm for both the red iron oxide milled with β-CD (40% of the total number of pigment particles) and the red iron oxide milled with CMC (38% of the total number of pigment particles) when compared to the distribution of hydrodynamic diameters for iron oxide milled without oligomeric and / or polymeric carbohydrates.

[0130] Surprising improvements were also achieved with white titanium dioxide and green chromium oxide. When compared to pigments milled under the same conditions but without additives, white titanium dioxide milled with β-CD, white titanium dioxide milled with CMC, and green chromium oxide milled with CMC each show a reduction in hydrodynamic diameter.

[0131] It can be noticed that some complexes according to the invention made by milling natural pigments with CMC have even smaller diameters relative to complexes obtained by milling the same pigments with β-CD.

[0132] Example 6: Determination of hydrodynamic diameter in slightly basic suspensions To assess the particle size and its distribution, the pigment complex obtained in Example 2 was suitably characterized by photon correlation spectroscopy.

[0133] 1 to 5 mg of each sample prepared in Example 2 was suspended in 4 ml of distilled water, and the same measurements as in Example 5 were carried out.

[0134] The samples were shaken anew and particle size was calculated by weighted averaging of nine consecutive experiments from a multimodal intensity distribution model.

[0135] Table 2 below shows the calculated hydrodynamic diameter (nanometer) distribution of pigment complexes in slightly basic suspensions (pH=7.5-8.5).

[0136] [Table 2]

[0137] Looking at Tables 1 and 2 together, it is clear that the particles obtained by milling the pigment with β-CD in conjunction with NaHCO3 generally have a smaller hydrodynamic diameter than the diameter of particles obtained by milling the pigment with β-CD without inorganic additives and dispersed in a neutral environment.

[0138] Example 7: Milling of natural pigments under neutral conditions (comparative) The procedure of Example 3 was carried out under the same milling conditions using only natural red iron oxide and NaOH without any oligomeric and / or polymeric carbohydrates, resulting in a milled pigment in the form of a red powder.

[0139] The powder thus obtained exhibited a slightly darker color when compared with the pigment complex according to the invention obtained in Example 3.

[0140] The above procedure was also carried out on natural yellow iron oxide, natural white titanium oxide, and green chromium oxide.

[0141] Example 8: Determination of Hydrodynamic Diameter in Basic Suspension To assess the particle size and its distribution, the pigment complex obtained in Example 3 was suitably characterized by photon correlation spectroscopy.

[0142] 1 to 5 mg of each sample prepared in Example 3 was suspended in 4 ml of distilled water, and the same measurements as in Example 5 were carried out.

[0143] The samples were shaken anew and particle size was calculated by weighted averaging of nine consecutive experiments from a multimodal intensity distribution model.

[0144] Table 3 below shows the calculated hydrodynamic diameter distribution of pigment complexes in weakly basic suspensions (pH=10-11).

[0145] The resulting pigment powder prepared in Example 7 was also suitably characterized by photon correlation spectroscopy to assess the particle size and its distribution.

[0146] Table 3 shows the calculated hydrodynamic diameter distribution of the milled pigment powders obtained in Examples 3 and 7 in weakly basic suspensions (pH=10-11).

[0147] [Table 3]

[0148] Looking at Tables 1, 2 and 3 together, it is clear that the particles obtained by milling the pigment with β-CD with NaOH generally have a hydrodynamic diameter that is smaller than not only the diameter of particles obtained by milling the pigment with β-CD without inorganic additives and dispersed in a neutral environment, but also, surprisingly, the diameter of particles obtained by milling the pigment with β-CD with NaHCO.

[0149] In particular, milling red iron oxide or green chromium oxide with β-CD and NaOH achieved a significant improvement over the composites obtained by milling the pigments with β-CD and NaHCO3 (less than 2% of particles with a hydrodynamic diameter less than 150 nm for particles obtained by milling red iron oxide, β-CD, and NaHCO3, versus approximately 58% for particles obtained by milling red iron oxide, β-CD, and NaOH).

[0150] For comparison, the particle size of a pigment milled by carrying out a process not in accordance with the present invention (Example 7) was also measured and is shown in Table 3.

[0151] As can be seen from Table 3, the particles obtained by milling the pigment with β-CD in conjunction with NaOH generally have smaller hydrodynamic diameters when compared to the diameter of the particles obtained by the procedure of Example 7.

[0152] Example 9: Preparation of pigment composites under basic conditions with increasing metal oxide content and determination of hydrodynamic diameter β-Cyclodextrin was added to the native metal oxide according to a mass ratio of metal oxide / carbohydrate equal to 2:1.

[0153] β-Cyclodextrin and natural white titanium dioxide were mixed together. NaHCO3 was added before milling.

[0154] The mass ratio between metal oxide, β-cyclodextrin and sodium bicarbonate was 4:2:1, respectively.

[0155] The mixture thus obtained was milled in a planetary ball mill (Retsch PM 100) at 550 rpm and using a ball to mass ratio equal to 9: 1. The milling process was carried out for 150 minutes.

[0156] This procedure was repeated under the same conditions by adding NaOH instead of NaHCO3.

[0157] The pigment composites thus obtained were suitably characterized by photon correlation spectroscopy to assess the particle size and its distribution.

[0158] 1 to 5 mg of each sample thus prepared was suspended in 4 ml of distilled water, and the same measurements as in Example 5 were carried out.

[0159] The samples were shaken anew and particle size was calculated by weighted averaging of nine consecutive experiments from a multimodal intensity distribution model.

[0160] The following Table 4 shows the calculated hydrodynamic diameter distributions of the complexes thus obtained in slightly basic and weakly basic suspensions, respectively.

[0161] [Table 4]

[0162] Surprisingly, by comparing the particle size distributions shown in Table 4 with those of the white titanium oxide composite (white titanium oxide, β-CD and NaHCO3) in Table 2 and the white titanium oxide (white titanium oxide, β-CD and NaOH) in Table 3, respectively, a significant reduction in hydrodynamic diameter is achieved when the amount of metal oxide is increased relative to the amount of both β-CD and inorganic additive.

[0163] Example 10: Preparation of pigment complexes under basic conditions with reduced ball-to-mass ratio and determination of hydrodynamic diameter Carboxymethylcellulose was added to natural yellow iron oxide according to a metal oxide / carbohydrate mass ratio equal to 1:2.

[0164] Carboxymethyl cellulose and natural yellow iron oxide were mixed.

[0165] The mixture thus obtained was milled in a planetary ball mill (Retsch PM 100) at 450 rpm and using a ball to mass ratio equal to 3: 1. The milling process was carried out for 180 minutes.

[0166] The pigment composites thus obtained were suitably characterized by photon correlation spectroscopy to assess the particle size and its distribution.

[0167] 1 to 5 mg of the sample thus prepared was suspended in 4 ml of distilled water, and the same measurement as in Example 5 was carried out.

[0168] The samples were freshly shaken and particle size was calculated by a weighted average of nine consecutive experiments from a multimodal intensity distribution model. pH was measured with a glass electrode.

[0169] The following Table 5 shows the calculated hydrodynamic diameter distribution of the complexes thus obtained in neutral suspension, respectively.

[0170] [Table 5]

[0171] Viewing Tables 1 and 5 together, it is clear that the composite obtained by milling yellow iron oxide with CMC at a ball-to-mass ratio of 10 has particles with a larger mean hydrodynamic diameter when compared to particles from the composite obtained by milling the same pigment with CMC at a ball-to-mass ratio of 6.

[0172] In particular, the composite obtained by milling yellow iron oxide with CMC at a ball-to-mass ratio of 10 has approximately 41% of the particles with a hydrodynamic diameter of less than 250 nm, while over 77% of the particles of the yellow iron oxide composite of Table 5 have a hydrodynamic diameter of less than 250 nm.

[0173] Example 11: Evaluation of striping effect in a liquid skin cosmetic composition for facial makeup First, a gel was prepared at 75°C from the disodium salt of EDTA (0.20 g), carbomer (0.80 g), water (90 ml), and yellow iron oxide milled with CMC (0.80 g) as prepared in Example 1, titanium dioxide milled with β-CD and NaOH (4.10 g) as prepared in Example 3, and red iron oxide milled with β-CD and NaOH (0.10 g) as prepared in Example 3.

[0174] An emulsion was prepared by adding Pemulen TR-1 (0.15 g) and ethylhexyl palmitate (3.00 g) to the gel using an industrial mixer. After 60 minutes, the emulsion was subsequently cooled. After cooling, Euxil PE9010 (0.90 g) preservative was added. Finally, the emulsion was homogenized.

[0175] A homogeneity test was carried out on the resulting neutral emulsion (pH 6-8) by the following method: a small drop of emulsion was placed between two glass plates, which were then slid over each other. The thin emulsion layer that separated from each other and remained on one of the glass plates was analyzed.

[0176] As shown in FIG. 1, the cosmetic emulsion obtained by using the mixture of pigment complexes according to the present invention is homogeneous and very gentle on the eyes.

[0177] In fact, the pigment complex was easily and stably dispersed in aqueous media, and then a stable emulsion was obtained, which had a strong colored hue and completely eliminated unwanted stripes.

[0178] Example 12: Sedimentation test of prepared solid pigments The settling properties of the following pigment complexes from Examples 1-3 were evaluated: red iron oxide milled with CMC in water at pH = 6-7 (Reference 1); red iron oxide milled with β-CD and NaHCO3 in water at pH = 7.5-8.5 (Reference 2); red iron oxide milled with β-CD and NaOH in water at pH = 11 (Reference 3).

[0179] In parallel, the settling properties of the following pigments not according to the invention obtained in Example 4 were evaluated: red iron oxide (Reference 4) dispersed and milled in water at pH=6-7.

[0180] Samples of the aforementioned pigment complex and pigment according to Example 4 were weighed at ∼5 mg into 5 ml glass vials, and 4 ml of water was added to each, after which the glass vials were closed and shaken at room temperature for 30 seconds in a parallel laboratory shaker at 120 rpm.

[0181] The photograph shown in Figure 2 was taken after 18 hours, the dispersion so obtained still being in that state at room temperature.

[0182] FIG. 3 shows the dispersions described above after an amount of liquid has been removed from each glass vial (the vial on the left) and placed in another vial (the vial on the right).

[0183] As is evident from FIG. 3, the pigment complex according to the invention did not adhere to the walls of the glass vial.

[0184] In contrast, when an amount of the dispersion of Reference 3 was removed from its glass vial, it was clear that the pigment not according to the invention had adhered to the glass wall of the container.

[0185] It is thus demonstrated that the pigment complex according to the invention does not adhere to glass and therefore avoids consequences that are highly undesirable and particularly frowned upon by consumers, especially cosmetic consumers.

[0186] Example 13: Preparation of a pigment complex under neutral conditions in a roll ball mill β-Cyclodextrin and carboxymethylcellulose were added to the natural metal oxide according to a mass ratio of metal oxide / carbohydrate equal to 7: 3. Red iron oxide supplied by Sun Chemical Company was used.

[0187] β-Cyclodextrin, carboxymethylcellulose, and natural metal oxides were mixed together and milled in the ceramic jar of a roll ball mill (Tencan GQM-2-5) using zirconia balls at a nominal 200 rpm according to a ball-to-mass ratio equal to 4.5:1. The milling process was carried out for 4 hours.

[0188] A fine red powder was obtained.

[0189] Both the β-cyclodextrin and carboxymethylcellulose procedures were then repeated for three other natural pigments at equal metal oxide / carbohydrate ratios and under the same milling conditions. The natural pigments used were as follows: yellow iron oxide, black iron oxide, and white titanium oxide (all metal oxides supplied by Sun Chemical Co.).

[0190] The total number of experiments under neutral conditions was four.

[0191] Example 14: Preparation of pigment complexes under neutral conditions in a roll ball mill using different milling materials The procedure of Example 13 using β-cyclodextrin and carboxymethylcellulose was repeated with four different types of natural pigments at equal metal oxide / carbohydrate ratios under the same milling conditions: yellow iron oxide, red iron oxide, black iron oxide, and white titanium oxide (all metal oxides supplied by Sun Chemical Company).

[0192] The total number of experiments under neutral conditions was four.

[0193] The procedure with both β-cyclodextrin and carboxymethylcellulose was then repeated using four other different types of milling media: zirconia balls in a zirconia jar, zirconia balls in a polymer perfluorinated jar, and stainless steel balls in a stainless steel jar.

[0194] The total number of experiments under neutral conditions was 12.

[0195] Example 15: Determination of Hydrodynamic Diameter in Neutral Suspension To assess the particle size and its distribution, the pigment complex obtained in Example 13 was suitably characterized by photon correlation spectroscopy.

[0196] 1-5 mg of each sample prepared in Example 13 was suspended in 4 ml of distilled water in a clear plastic cuvette (90° scattering of 675 nm laser light), and light scattering was measured using a Brookhaven 90Plus Particle Size Analyzer in accordance with ISO 22412:2017.

[0197] The samples were freshly shaken and particle size was calculated from a multimodal intensity distribution model by weighted averaging of nine consecutive experiments (data collection period: 30 s for each run).

[0198] Table 1 below shows the calculated hydrodynamic diameter (nanometer) distribution of pigment complexes in neutral suspension (pH=6-7).

[0199] Table 6 shows the calculated hydrodynamic diameter distribution of the milled pigment powder obtained in Example 13 under neutral conditions (pH=6-7).

[0200] [Table 6]

[0201] It is clear that the composites obtained by the process according to the present invention generally have different hydrodynamic diameter distributions for the red iron oxide particles. The hydrodynamic diameter distributions are significantly shifted to lower nanometers in all cases when compared to the hydrodynamic diameter distributions of iron oxides milled without the use of oligomeric and / or polymeric carbohydrates. The different milling media did not show essentially different hydrodynamic radius distributions.

Claims

1. 1. A process for the preparation of a composite comprising particles of a metal oxide pigment having a median diameter of less than 1 μm and an oligomeric and / or polymeric carbohydrate, comprising: a) providing a metal oxide pigment and an oligomeric and / or polymeric carbohydrate; b) grinding said metal oxide pigment and said oligomeric and / or polymeric carbohydrate in a ball mill under dry milling conditions to obtain a pigment composite comprising a metal oxide pigment having a median diameter of less than 1 μm and an outer surface partially or completely covered by said oligomeric and / or polymeric carbohydrate; the mass ratio between the metal oxide pigment and the oligomeric and / or polymeric carbohydrate provided in step a) is comprised between 1:10 and 10:1; and a base additive is added to and mixed with the metal oxide pigment before or during the milling step b), wherein the base additive comprises an inorganic base additive selected from the group consisting of alkali hydroxides, alkaline earth hydroxides, carbonates, bicarbonates, and any combination thereof.

2. 2. The process of claim 1, wherein the mass ratio between the metal oxide pigment and the oligomeric and / or polymeric carbohydrate is comprised between 1:5 and 5:

1.

3. 3. The process of claim 1 or 2, wherein the ball mill is selected from the group consisting of a planetary ball mill, a roll ball mill, and a cylindrical ball mill.

4. 4. The process according to any one of claims 1 to 3, wherein the grinding step b) is carried out with a ball to mass ratio comprised between 2:1 and 15:

1.

5. 5. The process of claim 4, wherein the grinding step b) is carried out with a ball to mass ratio comprised between 2:1 and 7:

1.

6. The process according to any one of claims 1 to 5, wherein the grinding step b) is carried out at a rotation speed of between 200 rpm and 700 rpm.

7. 7. The process of claim 6, wherein the grinding step b) is carried out at a rotation speed of between 300 rpm and 550 rpm.

8. 8. The process of any one of claims 1 to 7, wherein the grinding step b) is carried out for a time between 0.5 hours and 15 hours.

9. 9. The process of claim 8, wherein the grinding step b) is carried out for a time between 1 hour and 9 hours.

10. The process of any one of claims 1 to 9, wherein the metal oxide pigment is a transition metal oxide pigment.

11. 11. The process of claim 10, wherein the transition metal oxide pigment is selected from the group consisting of iron (III) oxide, diferric (III) oxide, iron (II) oxide, titanium oxide, chromium (III) oxide, manganese (IV) oxide, zinc oxide, cobalt (II) oxide, zirconium (IV) oxide, tungsten (VI) oxide, and any combination thereof.

12. 12. The process of any one of claims 1 to 11, wherein the oligomeric and / or polymeric carbohydrate is selected from the group consisting of ionic cellulose, non-ionic cellulose, carboxymethyl cellulose and its salts, starch, alginate, hyaluronate, chitosan, carrageenan, pectin, cyclodextrin, and any combination thereof.

13. 13. The process of claim 12, wherein the oligomeric and / or polymeric carbohydrate is a cyclodextrin.

14. 14. The process of claim 13, wherein the oligomeric and / or polymeric carbohydrate is β-cyclodextrin.

15. 13. The process of claim 12, wherein the oligomeric and / or polymeric carbohydrate is an ionic cellulose or a non-ionic cellulose.

16. 13. The process of claim 12, wherein the oligomeric and / or polymeric carbohydrate is carboxymethylcellulose or a salt thereof.

17. 17. The process of any one of claims 1 to 16, wherein the inorganic base additive is sodium hydroxide, sodium carbonate or sodium bicarbonate.

18. 18. The process of claim 17, wherein the weight ratio between the metal oxide pigment and the inorganic base additive is comprised between 1:2 and 10:

1.

19. 20. The process of claim 18, wherein the weight ratio between the metal oxide pigment and the inorganic base additive is comprised between 1:2 and 5:

1.

20. 2. The process of claim 1, wherein the base additive further comprises an organic base additive selected from an amino acid, an alkyl or arylalkyl amine, a hydroxyalkyl or (hydroxy)arylalkyl amine, a hydroxyalkyl or (hydroxy)arylalkyl urea, a hydroxyalkyl or (hydroxy)arylalkyl thiourea, or any combination thereof.

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