A method for preparing long-lasting synthetic mica powder

Abstract

This invention discloses a method for preparing long-lasting synthetic mica powder. Based on the characteristics of traditional synthetic mica powder, this invention utilizes a unique process design and combination, including rinsing and desorption purification, grinding, centrifugal sorting, spray drying, condensation modification, and airflow dispersion, to obtain a long-lasting synthetic mica powder with small particle size, high purity, low surface energy, and properties such as hydrophobicity, oleophobicity, UV resistance, and skin affinity. This powder can be directly used in cosmetics. Furthermore, the method of this invention features a simple process flow, low cost, and ease of large-scale production, providing a new approach for the high-value utilization of synthetic mica and the acquisition of higher-quality long-lasting cosmetics.

Description

Technical Field

[0001] This invention relates to synthetic mica production and processing technology, specifically to a method for preparing long-lasting synthetic mica powder, belonging to the field of synthetic mica production and processing technology. Background Technology

[0002] Mica is a natural mineral with a unique layered structure and physicochemical properties, widely used in various fields such as electronics, coatings, plastics, rubber, and cosmetics. Mica powder, in particular, is an ideal powder raw material for making face powders due to its flaky structure, insolubility in acids, alkalis, and organic solvents, and excellent skin adhesion. However, traditional natural mica has problems such as high heavy metal content, potential contamination with carcinogens like asbestos, and a dull color. Therefore, synthetic mica is gradually becoming a new alternative to natural mica.

[0003] Synthetic mica powder (i.e., fluorophlogopite powder) possesses hydrophilic surface properties due to the presence of hydroxyl groups (-OH). Furthermore, the presence of these hydroxyl groups fosters hydrogen bonding among the mica particles, resulting in smaller particle sizes, larger specific surface areas, and stronger hydrogen bonding. This leads to the tendency for synthetic mica powder to agglomerate into relatively hard particles. This property is detrimental to cosmetic applications, causing a rough skin feel. Additionally, cosmetics are generally mixtures with oils as the primary dispersion system. The hydrophilic surface of synthetic mica powder cannot be fully wetted by oils, making it difficult to disperse evenly in cosmetics. This results in reduced spreadability and coverage, leading to a poorer skin feel. Generally, cosmetics, once applied to the skin, need to maintain a certain level of staying power under daily activities, meaning they are not easily affected by water, sweat, or sebum, thus preventing makeup changes. On the other hand, due to the presence of hydroxyl groups on its surface, synthetic mica powder is usually weakly alkaline, which can easily cause dehydration, dryness, and peeling when applied to the skin. Healthy skin has a suitable pH level between 4 and 6. Slightly acidic conditions can resist allergens and maintain healthy skin.

[0004] In existing technologies, synthetic mica powder obtained through wet milling typically has a particle size of 10–15 μm, while the mica powder required for cosmetics usually has a particle size below 10 μm, with below 5 μm being optimal; particle size below 5 μm is also referred to as the ultrafine particle size range. Traditional wet milling processes struggle to obtain mica powder with an ultrafine particle size below 5 μm, primarily because they cannot address the hard agglomeration problem that occurs during the dehydration and drying process. Although dry milling can produce synthetic mica powder with a smaller particle size than wet milling, the lack of liquid wetting during dry milling leads to severe mechanical damage to the mica surface. Furthermore, the static electricity generated by friction and the inability to release additional surface energy make dry-milled synthetic mica powder more prone to hard agglomeration, resulting in a rough texture unsuitable for cosmetics. In addition, synthetic mica powder itself has high surface energy, and the smaller the particle size, the higher the surface energy and the stronger the hydrophilicity, making it more susceptible to agglomeration. The aforementioned technologies also cannot directly produce synthetic fluorophlogopite mica powder with low surface energy, hydrophobicity, and excellent dispersibility. Researchers have used liquid-phase deposition to coat the surface of synthetic fluorinated phlogopite powder with a layer of metal oxide (usually titanium dioxide, tin oxide, silicon dioxide, etc.), and then filter, wash, dry, and calcinate to dehydrate it to obtain synthetic mica with low surface energy. However, this process is complicated, has high production costs, and covers up the original surface properties of the mica. Summary of the Invention

[0005] To address the problem that existing synthetic mica powders, obtained through conventional methods, are prone to agglomeration due to their high surface energy and hydrophilicity, making them unsuitable for direct use in long-lasting cosmetics, this invention provides a method for preparing long-lasting synthetic mica powder. This invention addresses the characteristics of existing synthetic mica powders by employing methods such as rinsing and desorption purification, grinding, centrifugal separation, spray drying, condensation modification, and airflow dispersion to obtain long-lasting synthetic mica powder with characteristics such as small particle size, high purity, low surface energy, hydrophobicity, oleophobicity, UV resistance, and skin affinity, making it directly applicable to the production of cosmetics.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is specifically as follows:

[0007] A method for preparing a long-lasting synthetic mica powder, the method comprising the following steps:

[0008] 1) Disperse the synthetic mica flakes in water, then add a desorbent and stir. After stirring, grind and let stand. Then redisperse the precipitate in water and finally obtain mica slurry by centrifugation.

[0009] 2) The mica slurry is dried by spray drying to obtain mica powder.

[0010] 3) Dissolve the modifier in a solvent to obtain a modified solution, then mix the modified solution with mica powder evenly, then heat the mixture to react, and finally disperse the mixture to obtain a makeup-holding synthetic mica powder.

[0011] Preferably, the method further includes mica pretreatment, specifically: before step 1), the synthetic mica sheets are first subjected to acid leaching treatment, and after the acid leaching is completed, the synthetic mica sheets are filtered out and washed (preferably using pure water to wash away residual acid).

[0012] Preferably, the acid is one of hydrochloric acid, sulfuric acid, or nitric acid, and preferably a dilute nitric acid solution with pH < 1, and the acid leaching time is 0.5 to 24 hours.

[0013] Preferably, in step 1), the water is pure water or deionized water, preferably pure water.

[0014] Preferably, in step 1), the mass ratio of synthesized mica powder to water is 1:5 to 20, more preferably 1:8 to 15.

[0015] Preferably, in step 1), the desorbent is one or more of sodium silicate, sodium hydroxide, sodium tripolyphosphate, sodium pyrophosphate, sodium hexametaphosphate, and sodium stearate, and more preferably one or more of sodium hydroxide, sodium tripolyphosphate, and sodium pyrophosphate.

[0016] Preferably, in step 1), the amount of desorbent added is 0.1-1% of the total mass of the synthesized mica powder, preferably 0.2-0.8%.

[0017] It should be noted that in step 1), the purpose of the grinding process is to refine the mica flakes with a relatively large initial particle size. Any existing grinding technique is applicable. Preferably, in this invention, the grinding process specifically involves: grinding the mica flakes into powder using a vertical stirred mill, controlling the mass ratio of mica to pure water in the mill to be 5-10:2-3. The grinding media in the mill is zirconia beads, and the mica flakes are ground through the relative movement and shearing action of the zirconia beads. The grinding is carried out until the average particle size of the mica powder is <22 μm, with upper and lower limits of 1 μm and 45 μm, respectively.

[0018] Preferably, in step 1), the centrifugal sorting is carried out at a feed rate of 7–12 m / s. 3 / h (preferably 8-10m) 3 The mica slurry is obtained by sorting under the conditions of centrifugal differential speed of 4-6 (preferably 5-5.5) and rotation speed of not less than 3000 r / min (preferably 3000-3500 r / min).

[0019] Preferably, in step 1), the average particle size of mica in the mica slurry is 1 to 10 μm, more preferably 2 to 8 μm.

[0020] Preferably, in step 2), the spray drying involves spraying the mica slurry in an atomized manner while simultaneously blowing hot air along the spraying direction to evaporate and dry it, thereby obtaining mica powder with a water content of less than 1 wt%.

[0021] Preferably, in step 2), the flow rate of the mica slurry spraying is 0.5–5 L / min, more preferably 1–4 L / min. The hot air stream is hot air at 200–350°C, more preferably 250–300°C.

[0022] Preferably, in step 3), the modifier is one or more of polymethylhydrosiloxane, polydimethylsiloxane alcohol, hexyltrimethoxysilane, n-hexadecyltrimethoxysilane, triethoxyoctylsilane, tridecafluorooctyltriethoxysilane, retinoxytrimethylsilane, and aminopropyltriethoxysilane, and more preferably one or more of polymethylhydrosiloxane, polydimethylsiloxane alcohol, triethoxyoctylsilane, and tridecafluorooctyltriethoxysilane.

[0023] Preferably, in step 3), the solvent is one or more of water, ethanol, isopropanol, glycerol, and ethyl acetate, and more preferably one or more of pure water, ethanol, and ethyl acetate.

[0024] Preferably, in step 3), the mass concentration of the modifier in the modified solution is 1-30%, more preferably 6-25%.

[0025] Preferably, in step 3), the mass ratio of the modified solution to the mica powder is 1:3 to 20, more preferably 1:5 to 15. The modified solution is added by spraying under stirring conditions, wherein the addition rate of the modified solution is 2 to 5 L / min.

[0026] Preferably, in step 3), the heating reaction is carried out at 100–150°C for 1–12 hours. Preferably, the ambient pressure for the heating reaction is negative (preferably not lower than -24 kPa).

[0027] Preferably, in step 3), the dispersion treatment is performed by using gas with a gas pressure of 0.5 to 1 MPa while the feed rate is 1 to 5 kg / min.

[0028] Preferably, in step 3), the modified solution also contains a catalyst, which is one or more of hydrochloric acid, acetic acid, tartaric acid, citric acid, and 1,2-succinic acid, preferably one of hydrochloric acid, tartaric acid, and citric acid, and more preferably citric acid.

[0029] Preferably, in step 3), the amount of catalyst added is 0.05 to 2.5% of the total mass of the modified solution, and more preferably 0.1 to 2%.

[0030] Preferably, the makeup-holding synthetic mica powder has an average particle size of 1-10 μm, a whiteness of not less than 85, a pH of 4.5-6.5, a water contact angle of not less than 135°, and an activation degree of not less than 99%.

[0031] Preferably, the structure of the long-lasting synthetic mica powder is as follows: a synthetic mica core is formed, and a modified molecular layer is coated on the surface of the synthetic mica. The hydrophobic groups of the modified molecular layer face outwards, and the silicon atoms on its inner side form Si-O-Si bonds with the synthetic mica. Its surface bonding structure is shown below:

[0032]

[0033] Wherein, R is a hydrophobic functional group, preferably one or more of octyl, hexyl, tridecylfluorooctyl, n-hexadecyl, aminopropyl, and retinoxy.

[0034] In this invention, traditional synthetic mica flakes (obtained through in-house production or external purchase) are generally used as raw materials (the average particle size is generally preferably 4-16 mesh, with some fluctuation allowed in actual production). Based on their characteristics, they are subjected to targeted treatments including rinsing, desorption purification, grinding, centrifugal sorting, spray drying, condensation modification, and airflow dispersion. The final product is a makeup-grade synthetic mica powder with an average particle size of 1-10 μm, characterized by high purity, low surface energy, good dispersibility and non-agglomeration, hydrophobicity, oleophobicity, UV resistance, and skin affinity. This powder can be directly used in cosmetics. Furthermore, the process of this invention is simple and easy to operate, low in cost, and easily scalable for mass production.

[0035] In this invention, the particle size gap is calculated based on the upper limit Dv(90), lower limit Dv(10), and median particle size Dv(50) of mica in the mica slurry obtained by centrifugation according to the following formula: Particle size gap = [Dv(90) - Dv(10)] / Dv(50), as shown in the table below:

[0036] Serial Number Dv(10) Dv(50) Dv(90) Distance Mica powder 1 0.69μm 1.7μm 3.1μm 1.40 Mica powder 2 1μm 3.2μm 5.6μm 1.44 Mica powder 3 3.8μm 6.3μm 12.5μm 1.39

[0037] In this invention, traditional synthetic mica products generally contain impurities such as quartz, magnesium silicate, and fluorite, which are detrimental to the application of synthetic mica powder in cosmetics. Therefore, this invention utilizes water as a dispersant and cleaning agent, separating and removing impurities from the synthetic mica powder. Specifically, synthetic fluorophlogopite mica powder is dispersed in pure water, with a water-to-mica powder ratio that is as high as possible, typically between 1:5 and 1:15. After the synthetic mica powder is added to the water, it is stirred at high speed. The shear force generated by the velocity difference in the fluid field peels off the impurities adsorbed on the mica surface, dissolving them in the water. After standing for a period of time, solid-liquid separation is performed to remove the impurities. To improve the impurity removal effect, a small amount of desorbent (one or more of sodium silicate, sodium hydroxide, sodium tripolyphosphate, sodium pyrophosphate, sodium hexametaphosphate, sodium stearate, sodium dodecyl sulfate, and polyacrylamide) is added during the stirring and dispersion process of the synthetic mica powder. The addition of the desorbent further promotes the separation of impurities and improves the purity of the mica powder.

[0038] In this invention, water washing and desorption primarily remove soluble impurities from mica. Some insoluble impurities settle along with the mica and remain in the solid phase. Therefore, this invention further disperses the precipitate after rinsing, desorption, and grinding in water, utilizing the difference in particle size and specific gravity between the impurities and the mica powder to achieve further impurity removal. Specifically, this is achieved using centrifugal separation. The centrifugal separation process parameters are: a feed rate of 7–12 m / s². 3 The synthetic fluorophlogopite powder was sorted under conditions of centrifugal differential speed of 4-6 r / min and rotation speed of not less than 3000 r / min to remove coarser particles and impurities such as sand and gravel, resulting in a sorted synthetic fluorophlogopite powder with an average particle size of 2-10 μm. In other words, differential centrifugation effectively removed insoluble impurities as well as relatively large mica particles, thus achieving particle size regulation.

[0039] In this invention, the mica undergoes an acid leaching pretreatment before water washing and desorption. This acid leaching treatment removes acid-soluble impurities adsorbed on the mica flakes, primarily acid-soluble metal oxides and fluorides such as iron oxide, ferrous oxide, magnesium fluoride, and calcium fluoride. This effectively improves the purity of the mica powder.

[0040] In this invention, the mica slurry after centrifugal separation has a high water content (generally greater than 80%), making it a flowing slurry. Traditional methods involve filtration, collecting the filter cake, and then baking it to dry. However, this method is unsuitable for this product because smaller mica powder particles have a larger specific surface area and higher surface energy. Macroscopically, fine-particle mica powder is prone to agglomeration during baking, forming large agglomerates that are unsuitable for cosmetic production. Due to the adsorption of hydroxyl groups (-OH) on the mica surface, the agglomeration types that may occur under static baking include 1) hydrogen-bonded agglomeration, i.e., the interaction between hydroxyl groups; and 2) chemically bonded agglomeration, i.e., the formation of -O- chemical bonds. Once these agglomerates occur, they are almost impossible to break. Therefore, in the preparation method described in this invention, spray drying is used to achieve the drying and dehydration of the synthesized fluorophlogopite mica powder. The basic principle is to atomize the mica powder slurry. The atomization method can be high-pressure air spraying or centrifugal force to "splash" the liquid out in a mist. After atomization, the mica powder particles are dispersed in the mist, with the distance between them considered infinite (relative to their particle size). Hot air is then blown along the spray direction to remove moisture within 3-5 seconds, achieving drying and preventing agglomeration. The specific process generally involves: spraying the liquid material at a flow rate of 0.5-5 L / min, while simultaneously blowing hot air at 200-350°C along the spray direction to rapidly evaporate the moisture; and then using a cyclone separator to collect the dried synthetic fluorophlogopite powder (moisture content <1 wt%). Deviations in process parameters will result in insufficient drying and reduced dispersibility.

[0041] In this invention, the basic principle of surface modification is to utilize a chemical adsorption reaction to bond organic molecules with the hydroxyl groups adsorbed on the mica surface. The organic molecules cover the mica powder surface, with the oleophilic end facing outwards. The surface-modified synthetic fluorophlogopite powder then possesses various special properties such as oleophilicity, makeup retention, hydrophobicity, and UV resistance. The key to the modification process is the thorough mixing and contact between the modifier and the mica powder. Therefore, in this invention, the modifier needs to be pretreated before contacting the mica. Specifically, the modifier is fully dispersed in a solvent to form a modified solution: that is, the modifier is added to the solvent and dispersed evenly using a high-speed disperser (for example, dispersed for at least 30 minutes at a speed of 70-270 r / min). By pre-treating and activating the modifier into a uniformly dispersed solution before use (i.e., the prepared modifier solution is fully dispersed and emulsified by high-speed stirring, and a Si-OH intermediate is pre-reacted), the modifier solution is then added to a device containing mica powder via atomized spray under high-speed stirring (for example, the modifier solution is fed at a spray rate of 2-5 L / min at a rotation speed of 120-200 r / min, and after all the modifier solution has been sprayed, stirring continues for at least 30 minutes). In other words, this invention achieves thorough mixing and dispersion of the organic modifier and synthetic mica powder through the above process. The form of the modifier solution ensures the effectiveness of the reaction, and the process is simple.

[0042] In this invention, the modifier is one or more of polymethylhydrosiloxane, polydimethylsiloxane alcohol, hexyltrimethoxysilane, n-hexadecyltrimethoxysilane, triethoxyoctylsilane, tridecafluorooctyltriethoxysilane, retinoxytrimethylsilane, and aminopropyltriethoxysilane. Specifically, when tridecafluorooctyltriethoxysilane is used as one of the modifiers, it can further reduce the surface energy of the synthesized mica powder, giving it not only hydrophobicity but also oleophobicity (specifically, exhibiting both hydrophobicity and oleophobicity simultaneously, with a water contact angle >135° and an oil contact angle >100°). When retinoxytrimethoxysilane is used as one of the modifiers, it also possesses high-efficiency antioxidant properties, thus improving the product's antioxidant capacity, preventing product deterioration, and providing antioxidant effects when applied to cosmetics. It should be noted that, to improve the solubility of the modifier when dissolving it, a surfactant can be added for emulsification and dispersion; for example, the surfactant could be polysorbate 80.

[0043] In this invention, a catalyst is added to the modification solution to further improve the modification effect. Under the action of the catalyst, the uniformly dispersed modifier and mica powder are mixed and heated (generally 100-150℃) to cause the modifier to undergo a dehydration condensation reaction with the hydroxyl groups adsorbed on the mica surface (reaction time is generally 1-12 hours). The reaction formula is: R1-Si(OC2H5)3 + HO-Mica → R1-Si-O-Mica + 3C2H5OH. Specifically, a negative pressure (e.g., a vacuum degree of not less than -24 kPa) should be applied during the condensation reaction. The specific method is to use a heating oven with sealing strips and a vacuum pump. The purpose of applying a negative vacuum degree is that, since the condensation reaction is a reversible reaction and the alcohols in the reaction products are volatile, the negative vacuum can promote the volatilization of alcohols, causing the reaction equilibrium to continuously move to the right.

[0044] In this invention, after the dehydration condensation reaction, the modified mica powder needs to be redispersed. Specifically, this is done by using an airflow disperser to treat the synthesized fluorophlogopite powder after the reaction. The airflow breaks up the aggregated particles, improving dispersibility and making the product meet the requirements of a lightweight, skin-feeling cosmetic. The specific dispersion process involves using gas at a pressure of 0.5–1 MPa at a feed rate of 1–5 kg / min for airflow dispersion, and collecting the target product using a cyclone separator.

[0045] In this invention, the makeup-holding synthetic mica powder prepared by the method described herein possesses excellent hydrophobicity, with a water contact angle of not less than 135° (preferably exceeding 140°), a whiteness of not less than 85, a pH of 4.5–6.5, and an activation degree of 99% (the specific testing method involves placing M grams of the product in pure water, stirring and shaking thoroughly, then allowing it to stand to remove powder floating on the surface. The settled powder is filtered out, dried, and weighed to obtain m grams; the activation index is calculated as H = (-m) / M × 100%. An activation degree > 99 indicates that more than 99% of the powder's surface properties have been altered due to the process described in this invention). The specific structure of this makeup-holding synthetic mica powder is as follows: It has synthetic mica as its core, with a modified molecular layer coating the surface of the synthetic mica. The hydrophobic groups of the modified molecular layer face outwards, and the silicon atoms on its inner side form Si-O-Si bonds with the synthetic mica. Its surface bonding structure is shown below:

[0046]

[0047] Wherein, R is a hydrophobic functional group, preferably one or more of octyl, hexyl, tridecylfluorooctyl, n-hexadecyl, aminopropyl, and retinoxy.

[0048] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0049] 1. Based on the characteristics of traditional synthetic mica powder, this invention uses a special process design, specifically through rinsing and desorption purification, grinding, centrifugal separation, spray drying, condensation modification, and airflow dispersion, to obtain a makeup-holding synthetic mica powder with small particle size, high purity, low surface energy, and characteristics such as hydrophobicity, oleophobicity, UV resistance, and skin affinity, which can be directly used in the production of cosmetics.

[0050] 2. The method of the present invention has a simple process flow, low cost, and is easy to scale up for production, providing a new way for the high-value utilization of synthetic mica and obtaining better quality long-lasting cosmetics. Attached Figure Description

[0051] Figure 1 This is a microscopic image of the particle size distribution of the synthetic mica powder obtained in Example 3 of the present invention.

[0052] Figure 2 The image shows the X-ray diffraction pattern of the synthetic mica powder prepared in Example 3 of this invention.

[0053] Figure 3 The graph shows the hydrophobicity test results of the synthetic mica powder prepared in Example 3 of this invention.

[0054] Figure 4 These are comparative photos showing the activation degree test results of the synthetic mica powder prepared in Example 3 of this invention before and after modification.

[0055] Figure 5 This is a flowchart illustrating the overall process flow of the method described in this invention. Detailed Implementation

[0056] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments.

[0057] Example 1

[0058] Synthetic mica flakes after wind classification were selected and screened using a double-layer sieve. Mica flakes with a size range of 4 to 16 mesh were collected and soaked in a dilute nitric acid solution with pH < 1 for 12 hours. Then, the flakes were filtered, washed three times with pure water, and dried to obtain synthetic mica flakes.

[0059] First, weigh 100 kg of the above-mentioned synthetic mica flakes and put them into a rinsing vessel equipped with a stirrer, then add 1000 L of purified water. Start the stirrer to completely disperse the mica powder in the water to form a slurry. Add a mixture of 0.1 kg sodium hydroxide and 0.2 kg sodium pyrophosphate to the slurry and continue stirring for 60 minutes. After stirring, grind the mixture and then let it stand for 24 hours to allow the mica powder to precipitate. At this time, the upper layer of liquid is observed to be a yellowish-brown suspension, with a turbidity of approximately 22 NTU measured by a turbidimeter. Open the drain port on the side of the rinsing vessel to drain the upper layer of liquid until the synthetic mica powder precipitated at the bottom is exposed. The mica powder is observed to be a glossy white. Add another 850 L of purified water and continue stirring to dissolve and disperse the precipitated synthetic mica powder to form a slurry. Then, centrifuge the slurry: use a screw pump for feeding, maintaining a flow rate of 8.5 ± 0.5 m / s. 3 / h, adjust the centrifuge main unit speed to 3500r / min, maintain a differential speed of 5.3±0.1; collect the suspension to obtain the target mica slurry, and its average particle size was detected to be approximately 1.78μm.

[0060] Next, the mica slurry obtained above was injected into a spray dryer, the feed flow rate was adjusted to 1L / min, the temperature of the drying hot air was 290℃, and the dried mica powder was collected. Its moisture content was measured to be about 0.82%.

[0061] Then weigh out 15 kg of ethanol, 5 kg of purified water, and 0.05 kg of citric acid, mix and stir to dissolve. Then add 3 kg of triethoxyoctylsilane and pour the prepared solution into a high-speed mixer. Set the stirring speed to 220 r / min and stir for 1.5 hours to obtain the modifier solution.

[0062] Next, 100 kg of spray-dried synthetic mica powder was added to a mixer, and the mixer was started at a speed of 80 r / min. The modifier solution was then sprayed into the mixer at a flow rate of approximately 2 L / min. During spraying, the mixing speed was gradually increased to 180 r / min. After all the modifier solution had been sprayed, mixing continued for 2 hours. The mica powder mixed with the modifier was then discharged from the mixer, placed in a stainless steel tray, and placed in a preheated reaction vessel for a condensation reaction (the ambient pressure was controlled at -24 kPa during the reaction). The reaction temperature was set at 130℃, and the reaction time was 6 hours. During this time, the material was loosened every hour using a stainless steel rake. After the reaction was complete, the material was removed.

[0063] The reacted materials are fed into an airflow disperser for dispersing and deagglomeration. The feed rate is 2.5 kg / min, and the blower airflow pressure is adjusted to 0.7 MPa. The soft agglomerates generated during the baking process are broken up by the high-speed airflow and collected at a cyclone separator to obtain the surface-modified synthetic fluorophlogopite powder product.

[0064] Example 2

[0065] Repeat Example 1, except that 3 kg of triethoxyoctylsilane is replaced with 3 kg of tridecafluorooctyltriethoxysilane.

[0066] Example 3

[0067] Repeat Example 1, except that 3 kg of triethoxyoctylsilane is replaced with 3 kg of polymethylhydrosiloxane.

[0068] Example 4

[0069] Repeat Example 1, except that 3 kg of triethoxyoctylsilane is replaced with 3 kg of polydimethylsiloxane alcohol.

[0070] Example 5

[0071] Repeat Example 1, except that instead of soaking the mica sheets in a dilute nitric acid solution with pH < 1 for 12 hours, soak the mica sheets in a dilute hydrochloric acid solution with pH < 3 for 6 hours.

[0072] Example 6

[0073] Repeat Example 1, except that instead of soaking the mica sheets in a dilute nitric acid solution with pH < 1 for 12 hours, soak the mica sheets in a mixed solution of dilute hydrochloric acid and dilute sulfuric acid with pH < 1 for 12 hours.

[0074] Example 7

[0075] Repeat Example 1, except that the mixture of 0.3 kg sodium hydroxide and sodium pyrophosphate is replaced with 0.3 kg sodium silicate.

[0076] Example 8

[0077] Repeat Example 1, except that the mixture of 0.3 kg sodium hydroxide and sodium pyrophosphate is replaced with a mixture of 0.1 kg sodium silicate and 0.2 kg sodium tripolyphosphate.

[0078] Example 9

[0079] Repeat Example 2, except that 0.05 kg of citric acid is replaced with 0.15 kg of acetic acid.

[0080] Example 10

[0081] Repeat Example 2, except that 0.05 kg of citric acid is replaced with 0.15 kg of citric acid.

[0082] Example 11

[0083] Repeat Example 2, except that 0.05 kg of citric acid is replaced with 0.02 kg of citric acid.

[0084] Example 12

[0085] Repeat Example 10, except that 0.15 kg of citric acid is replaced with 0.15 kg of tartaric acid.

[0086] Example 13

[0087] Repeat Example 4, except that 3 kg of polydimethylsiloxane alcohol is replaced with 0.1 kg of polydimethylsiloxane alcohol.

[0088] Example 14

[0089] Repeat Example 4, except that 3 kg of polydimethylsiloxane alcohol is replaced with 1 kg of polydimethylsiloxane alcohol.

[0090] Example 15

[0091] Repeat Example 4, except that 3 kg of polydimethylsiloxane alcohol is replaced with 2 kg of polydimethylsiloxane alcohol.

[0092] Example 16

[0093] Repeat Example 4, except that 3 kg of polydimethylsiloxane alcohol is replaced with 4 kg of polydimethylsiloxane alcohol.

[0094] Example 17

[0095] Repeat Example 1, except that the mica sheets are not soaked in dilute nitric acid.

[0096] Comparative Example 1

[0097] Repeat Example 1, except that sodium hydroxide and sodium pyrophosphate are not added to the slurry.

[0098] Comparative Example 2

[0099] Repeat Example 2, except without adding citric acid.

[0100] Comparative Example 3

[0101] Repeat Example 4, except without adding polydimethylsiloxane alcohol.

[0102] Comparative Example 4

[0103] Repeat Example 4, except that ethanol, purified water, citric acid, triethoxyoctylsilane and 100 kg of spray-dried synthetic mica powder are added together into a mixing mixer.

[0104] The table below compares the performance parameters of the products obtained in the above embodiments and comparative examples:

[0105] Whiteness activation degree Water contact angle Oil absorption pH Example 1 93.8 96.5 135.5° 42 / 100 5.9 Example 2 93.5 99.4 141.0° 29 / 100 6.2 Example 3 93.9 100 149.2° 26 / 100 6.0 Example 4 93.1 97.2 123.4° 40 / 100 6.1 Example 5 84.9 96.9 138.1° 43 / 100 6.3 Example 6 86.8 95.9 136.9° 45 / 100 6.2 Example 7 84.5 97.9 139.3° 39 / 100 6.2 Example 8 91.2 98.0 139.9° 38 / 100 6.1 Example 9 91.2 82.9 121.3° 58 / 100 6.8 Example 10 90.5 99.4 144.7° 28 / 100 5.5 Example 11 90.8 71.2 91.5° 57 / 100 6.9 Example 12 90.8 94.2 133.1° 47 / 100 5.8 Example 13 89.7 77.4 89.9° 58 / 100 6.2 Example 14 88.2 86.1 128.4° 51 / 100 6.1 Example 15 90.0 97.9 139.3° 39 / 100 6.2 Example 16 90.1 99.9 145.8° 27 / 100 6.2 Example 17 78.3 95.5 135.8° 45 / 100 5.9 Comparative Example 1 81.6 91.1 124.7° 51 / 100 6.1 Comparative Example 2 90.9 67.6 89.9° 59 / 100 7.4 Comparative Example 3 93.6 0 0 71 / 100 7.3 Comparative Example 4 92.9 27.9 0 64 / 100 6.2

[0106] The table above shows that modifying mica with modifiers significantly affects the product's activation degree, water contact angle, and pH value. Furthermore, the method and amount of modifier used also have a significant impact on the results. In addition, the use and selection of catalysts during the modification process also significantly affect the modification outcome. It should also be noted that whether or not the initial mica flakes undergo acid leaching and desorption treatment not only significantly affects the product's whiteness but also influences the subsequent modification effect on the mica.

Claims

1. A method for preparing long-lasting synthetic mica powder, characterized in that: The method includes the following steps: 1) The synthetic mica flakes are dispersed in water, then a desorbent is added and stirred. After stirring, the flakes are ground and allowed to stand. The precipitate is then redispersed in water and finally separated by centrifugation to obtain mica slurry. The desorbent is sodium hydroxide and sodium pyrophosphate. 2) The mica slurry is dried by spray drying to obtain mica powder; 3) Dissolve the modifier in a solvent to obtain a modified solution, then mix the modified solution with mica powder evenly, then heat the mixture to react, and finally disperse the mixture to obtain a makeup-holding synthetic mica powder; the modified solution is added by spraying under stirring conditions. In step 3), the modifier is one or more of polymethylhydrosiloxane, polydimethylsiloxane alcohol, triethoxyoctylsilane, and tridecafluorooctyltriethoxysilane; the solvent is one or more of water, ethanol, isopropanol, glycerol, and ethyl acetate; the modified solution also contains a catalyst, which is citric acid; the amount of catalyst added is 0.1-2% of the total mass of the modified solution. The method also includes mica pretreatment, specifically: before step 1), the synthetic mica sheets are first subjected to acid leaching, and after the acid leaching is completed, the synthetic mica sheets are filtered out and washed.

2. The method according to claim 1, characterized in that: The acid used in the acid leaching process is one of hydrochloric acid, sulfuric acid, or nitric acid.

3. The method according to claim 2, characterized in that: The acid used in the acid leaching step is a dilute nitric acid solution with a pH < 1, and the acid leaching time is 0.5~24h.

4. The method according to any one of claims 1-3, characterized in that: In step 1), the water is pure water or deionized water.

5. The method according to claim 4, characterized in that: In step 1), the mass ratio of synthesized mica sheets to water is 1:5~20; and / or In step 1), the amount of desorbent added is 0.1-1% of the total mass of the synthesized mica sheets.

6. The method according to claim 5, characterized in that: In step 1), the mass ratio of synthesized mica sheets to water is 1:8~15; and / or In step 1), the amount of desorbent added is 0.2 to 0.8% of the total mass of the synthesized mica sheets.

7. The method according to any one of claims 1-3 and 5-6, characterized in that: In step 1), the centrifugal sorting is performed at a feed rate of 7~12m / s. 3 Mica slurry was obtained by sorting under conditions of / h and a rotation speed of not less than 3000r / min.

8. The method according to claim 7, characterized in that: In step 1), the centrifugal sorting is performed at a feed rate of 8-10 m / s. 3 Mica slurry was obtained by sorting under conditions of 3000~3500 r / min and 1 h.

9. The method according to claim 8, characterized in that: The average particle size of mica in mica slurry is 1~10μm.

10. The method according to claim 9, characterized in that: The average particle size of mica in mica slurry is 2~8μm.

11. The method according to any one of claims 1-3, 5-6, and 8-10, characterized in that: In step 2), the spray drying involves spraying mica slurry in an atomized manner while simultaneously blowing hot air along the spraying direction to evaporate and dry it, thereby obtaining mica powder with a water content of less than 1 wt%.

12. The method according to claim 11, characterized in that: The flow rate of the mica slurry injection is 0.5~5L / min; the hot air stream is hot air at 200~350℃.

13. The method according to claim 12, characterized in that: The flow rate of the mica slurry is 1~4 L / min; the hot air stream is hot air at 250~300℃.

14. The method according to any one of claims 1-3, 5-6, 8-10, and 12-13, characterized in that: In step 3), the solvent is one or more of pure water, ethanol, and ethyl acetate.

15. The method according to claim 14, characterized in that... The mass concentration of the modifier in the modified solution is 1-30%; and / or The mass ratio of the modified solution to mica powder is 1:3~20; the addition rate of the modified solution is 2~5L / min.

16. The method according to claim 15, characterized in that... The mass concentration of the modifier in the modified solution is 6-25%; and / or The mass ratio of the modified solution to mica powder is 1:5~15.

17. The method according to any one of claims 1-3, 5-6, 8-10, 12-13, and 15-16, characterized in that: In step 3), the heating reaction is carried out at 100-150°C for 1-12 hours; and / or The dispersion process involves using gas at a pressure of 0.5-1 MPa while feeding at a rate of 1-5 kg / min.

18. The method according to claim 17, characterized in that: The ambient pressure for the heating reaction is negative.

19. The method according to claim 18, characterized in that: The negative pressure is not lower than -24 kPa.

20. The method according to any one of claims 1-3, 5-6, 8-10, 12-13, 15-16, and 18-19, characterized in that: The structure of the long-lasting synthetic mica powder is as follows: It has synthetic mica as its core, and a modified molecular layer is coated on the surface of the synthetic mica; wherein the hydrophobic groups of the modified molecular layer face outwards, and the silicon atoms on its inner side form Si-O-Si bonds with the synthetic mica; its surface bonding structure is shown below: ； Wherein, R is octyl or tridecylfluorooctyl.

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