Solid hair dyeing composition based on 5, 6-dihydroxyindole and preparation method thereof

Abstract

The invention belongs to the technical field of hair dyes, and particularly relates to a solid hair dyeing composition based on 5, 6-dihydroxyindole and a preparation method thereof.The composition comprises a surfactant, 5, 6-dihydroxyindole, a reducing agent, a forming auxiliary, a structure stabilizer, a flow modifier and the balance water, and the water content of the composition is smaller than or equal to 0.5%. The preparation method comprises the following steps: mixing and melting the surfactant, the forming aid and the structure stabilizer; cooling and then adding embedded or unembedded 5, 6-dihydroxyindole and a reducing agent; adding a flow modifier; and pressing and forming. Through multiple synergistic effects of an anhydrous system, reducing agent protection, structure densification and oxygen isolation packaging, oxidative polymerization of the 5, 6-dihydroxyindole in the storage process is effectively inhibited, and the activity retention rate can reach 90% or above after the 5, 6-dihydroxyindole is stored at normal temperature for 12 months; strong base and strong oxidant are not needed in the hair dyeing process, the hair quality and strength retention rate after dyeing is high, and excellent safety and market application prospects are achieved.

Description

Technical Field

[0001] This invention belongs to the field of hair dye technology, specifically relating to a solid hair dye composition based on 5,6-dihydroxyindole and its preparation method. Background Technology

[0002] Dyeing gray hair black is one of the most stable and widely used consumer scenarios for hair dye products. Existing commercial hair dye products mainly rely on p-phenylenediamine-based oxidative dye systems. These products typically require strongly alkaline conditions and strong oxidants such as hydrogen peroxide to complete the dyeing reaction. Although the dyeing efficiency is high, they generally have problems such as strong irritation to the scalp and hair, high risk of sensitization, and damage to the hair keratin structure, and are gradually failing to meet consumers' demands for safety and gentleness.

[0003] 5,6-Dihydroxyindole (DHI) is an important precursor molecule of natural melanin in the human body. In the presence of oxygen, it can undergo spontaneous oxidative polymerization to generate a high-molecular-weight pigment with a structure highly consistent with natural melanin. Hair dyeing methods based on this mechanism are not traditional "exogenous dye coloring," but rather generate melanin polymers in situ on the surface and inside the hair fiber. Therefore, they have significant advantages in terms of biocompatibility and safety, and are considered an important technological direction to replace traditional oxidative hair dyeing systems.

[0004] However, DHI molecules are highly sensitive to moisture and oxygen. Even under weakly neutral conditions, the presence of trace amounts of moisture and air can cause uncontrollable premature oxidation and polymerization, leading to darker color, reduced activity, or even complete inactivation. This problem is particularly prominent during the product's storage, transportation, and sales cycle, and is a core technological bottleneck restricting the large-scale commercial application of DHI-based hair dye products.

[0005] Currently, most commercially available DHI hair dye products use aerosol cans or vacuum bottles to store the DHI-containing liquid or paste system in a sealed, inert gas environment. This largely isolates the product from air and slows down the oxidation reaction of DHI. While this method technically verifies the crucial role of "oxygen isolation" in DHI stability, it places extremely high demands on packaging structure and production conditions, resulting in high costs, inconvenient transportation, large packaging volume, and strict safety regulations, making it difficult to promote and apply in a wider range of consumer scenarios.

[0006] Besides aerosol cans, existing publicly available technologies attempt to formulate DHI into products in the form of creams, liquids, gels, or foams. However, these systems inevitably contain high moisture content, and the packaging forms are difficult to effectively isolate oxygen over a long period. Under normal storage conditions, air can still slowly diffuse in through the packaging materials or the interior of the system, causing DHI to continuously oxidize and deactivate during storage, thus making it difficult to meet the required shelf life of the product.

[0007] Further research revealed that even when DHI is simply converted from a liquid to a solid state, without systematic control over the system's moisture content, oxygen diffusion pathways, and microstructure, DHI will still gradually undergo oxidative polymerization due to the presence of trace amounts of moisture and oxygen. Therefore, simply relying on changes in packaging or physical state cannot fundamentally solve the long-term stability problem of DHI.

[0008] Based on the current state of the technology, there is an urgent need to develop a DHI hair dye product that does not rely on high-cost aerosol can packaging, can effectively inhibit the oxidation and deactivation of DHI under normal storage and transportation conditions, and only undergoes a dyeing reaction after being activated by water during the use stage, so as to achieve a balance between long-term stable storage, safe and gentle hair dyeing, and good industrial applicability. Summary of the Invention

[0009] To address the problems mentioned in the background art, this invention proposes a solid hair dye composition based on 5,6-dihydroxyindole and its preparation method. Through the synergistic effect of multiple processes including "anhydrous system + low-alkali environment + reducing agent protection + structural densification + oxygen-barrier encapsulation", the oxidative polymerization of 5,6-dihydroxyindole is effectively inhibited during storage. After 6–12 months of storage at room temperature, the activity retention rate can reach over 90%, thus solving the technical problem of the difficulty in the stable existence of this component in hair dye products.

[0010] The technical solution adopted by this invention to solve its technical problem is: to provide a solid hair dye composition based on 5,6-dihydroxyindole, comprising the following components by weight percentage:

[0011] 5,6-Dihydroxyindole 0.1–3.0 wt%

[0012] Reducing agent 0.05–5.0 wt%

[0013] Surfactant 10.0–75.0 wt%

[0014] Molding aids 10.0–50.0 wt%

[0015] Structural stabilizer 0.5–30.0 wt%

[0016] Flow modifier 0–5.0 wt%

[0017] The remainder is water.

[0018] in:

[0019] a) The composition has a solid molded structure and its moisture content is not higher than 0.5 wt%;

[0020] b) The 5,6-dihydroxyindole exists in the solid molded structure in an embedded and / or unembedded form;

[0021] c) The reducing agent and the 5,6-dihydroxyindole form a locally reducing microenvironment in the solid molded structure, thereby inhibiting the oxidative polymerization reaction of 5,6-dihydroxyindole under storage conditions, so that after the composition is sealed and stored at room temperature for 12 months, the activity retention rate of 5,6-dihydroxyindole is not less than 90%.

[0022] Furthermore, the surfactant includes sodium lauroyl glutamate, sodium cocoyl glycinate, sodium cocoyl methyl taurate, sodium cocoyl hydroxyethyl sulfonate, cocamidopropyl betaine, and / or C8-C16 alkyl glycosides.

[0023] Furthermore, the reducing agent includes ascorbic acid, sodium ascorbate, isoascorbic acid and its salts, sulfites, bisulfites, dithionites, thiosulfates, cysteine, or glutathione.

[0024] Furthermore, the molding aids include cetyl alcohol, stearyl alcohol, stearic acid, glyceryl stearate, glyceryl monostearate, beeswax, or carnauba wax.

[0025] Furthermore, the structural stabilizer includes xanthan gum, sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, or polyvinylpyrrolidone.

[0026] Furthermore, the flow modifier includes silica, talc, or microcrystalline cellulose.

[0027] This invention also provides a method for preparing a solid hair dye composition based on 5,6-dihydroxyindole, comprising the following steps:

[0028] S1. Control the moisture content of the reaction system. Under anhydrous or low-moisture conditions, mix and melt the surfactant, molding aid, and structural stabilizer to obtain a molten matrix.

[0029] S2. Cool the molten matrix to a suitable temperature, add embedded or unembedded 5,6-dihydroxyindole and a reducing agent, and mix thoroughly.

[0030] S3. Add the flow modifier to the mixture obtained in step S2 and mix thoroughly;

[0031] S4. Place the mixture obtained in step S3 into a mold and compact it under a certain pressure;

[0032] S5. Cool and demold to obtain a solid hair dye composition.

[0033] Furthermore, in step S1, the moisture content of the reaction system is ≤0.3wt%.

[0034] Furthermore, in step S2, the suitable temperature after the molten matrix is ​​cooled is no higher than 45°C.

[0035] Furthermore, the 5,6-dihydroxyindole exists in an encapsulated form, wherein the encapsulation method is at least one of the following:

[0036] (1) Glassy embedding of sugar alcohols: 5,6-dihydroxyindole is dissolved in erythritol and / or sorbitol system and dried under reduced pressure to form a glassy solid;

[0037] (2) Lipid microcapsule encapsulation: using beeswax and / or fatty acid glycerides as wall materials, 5,6-dihydroxyindole is encapsulated to form microcapsules by melt dispersion method;

[0038] (3) Polyol solid solution embedding: 5,6-dihydroxyindole is formed into a solid solution in anhydrous glycerol or propylene glycol.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] (1) This invention effectively inhibits the oxidative polymerization of 5,6-dihydroxyindole during storage through the synergistic effect of "anhydrous system + low-alkali environment + reducing agent protection + structural densification + oxygen-barrier encapsulation". After 6–12 months of storage at room temperature, the activity retention rate can reach more than 90%, which solves the technical problem that this ingredient is difficult to exist stably in hair dye products.

[0041] (2) When the product of the present invention is used, it is activated by water. 5,6-dihydroxyindole is oxidized in situ on the hair to generate a high molecular weight substance with the same structure as the natural melanin in the human body. The hair dyeing process does not require strong alkali or strong oxidant, and it does not irritate or cause allergic reactions to the scalp. The hair quality is well maintained after dyeing, and the strength retention rate is as high as 98% or more.

[0042] (3) The product of this invention is in solid form, requires no preservatives, and is easy to package, transport and carry; the preparation process is simple and the temperature control is friendly, making it suitable for industrial mass production and having good market application prospects. Attached Figure Description

[0043] Figure 1 The results are for the test of the hair dye composition prepared in Example 1. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] formula:

[0047] Surfactant: Sodium lauroyl glutamate 69.2 wt%

[0048] 5,6-Dihydroxyindole (unencapsulated): 1.5 wt%

[0049] Reducing agent: Ascorbic acid 2.0 wt%

[0050] Molding aid: Cetyl alcohol 20.0 wt%

[0051] Structural stabilizer: xanthan gum 5.0 wt%

[0052] Flow modifier: 2.0 wt% silica

[0053] Water content: 0.3 wt%

[0054] Preparation method:

[0055] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium lauroyl glutamate, cetyl alcohol, and xanthan gum, and heat to melt at 75℃ to obtain a molten matrix.

[0056] S2. Cool the molten matrix to 40°C, add the unencapsulated 5,6-dihydroxyindole and ascorbic acid, and mix thoroughly.

[0057] S3. Add silicon dioxide to the mixture obtained in step S2 and mix thoroughly.

[0058] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 5MPa.

[0059] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0060] Example 2

[0061] formula:

[0062] Surfactant: Sodium cocoyl glycinate 65.0 wt%

[0063] 5,6-Dihydroxyindole (sugar alcohol glassy encapsulation): 2.0 wt%

[0064] Reducing agent: Sodium sulfite 1.0 wt%

[0065] Molding aid: stearyl alcohol 27.3 wt%

[0066] Structure stabilizer: Sodium carboxymethyl cellulose 3.0 wt%

[0067] Flow modifier: talc 1.5 wt%

[0068] Water content: 0.2 wt%

[0069] Preparation method:

[0070] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl glycinate, stearyl alcohol, and sodium carboxymethyl cellulose, and heat to melt at 80℃ to obtain a molten matrix.

[0071] S2. Cool the molten matrix to 42°C, add the sugar alcohol glass-encapsulated 5,6-dihydroxyindole and sodium sulfite, and mix thoroughly.

[0072] S3. Add talc powder to the mixture obtained in step S2 and mix well;

[0073] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 6MPa.

[0074] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0075] Example 3

[0076] formula:

[0077] Surfactant: Sodium cocoyl methyl taurate 65.9 wt%

[0078] 5,6-Dihydroxyindole (lipid microcapsule encapsulation): 0.5 wt%

[0079] Reducing agent: cysteine ​​0.5 wt%

[0080] Molding aid: Stearic acid 30.0 wt%

[0081] Structure stabilizer: 2.0 wt% hydroxypropyl methylcellulose

[0082] Flow modifier: 1.0 wt% microcrystalline cellulose

[0083] Water content: 0.1 wt%

[0084] Preparation method:

[0085] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl methyl taurate, stearic acid, and hydroxypropyl methylcellulose, and heat to melt at 78℃ to obtain a molten matrix.

[0086] S2. Cool the molten matrix to 38°C, add 5,6-dihydroxyindole and cysteine ​​encapsulated in lipid microcapsules, and mix thoroughly.

[0087] S3. Add microcrystalline cellulose to the mixture obtained in step S2 and mix thoroughly.

[0088] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 4MPa.

[0089] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0090] Example 4

[0091] formula:

[0092] Surfactant: Sodium cocoyl hydroxyethyl sulfonate 69.0 wt%

[0093] 5,6-Dihydroxyindole (polyol solid solution encapsulation): 1.0 wt%

[0094] Reducing agent: glutathione 0.8 wt%

[0095] Molding aid: 22.3 wt% glyceryl monostearate

[0096] Structure stabilizer: Polyvinylpyrrolidone 4.0 wt%

[0097] Flow modifier: 2.5 wt% silica

[0098] Water content: 0.4 wt%

[0099] Preparation method:

[0100] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl hydroxyethyl sulfonate, glyceryl monostearate, and polyvinylpyrrolidone, and heat to melt at 82℃ to obtain a molten matrix.

[0101] S2. Cool the molten matrix to 41°C, add 5,6-dihydroxyindole and glutathione embedded in polyol solid solution, and mix evenly.

[0102] S3. Add silicon dioxide to the mixture obtained in step S2 and mix thoroughly.

[0103] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 7MPa.

[0104] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0105] Example 5

[0106] formula:

[0107] Surfactant: C8 alkyl glycoside 70.0 wt%

[0108] 5,6-Dihydroxyindole (unencapsulated): 0.8 wt%

[0109] Reducing agent: Sodium isoascorbate 1.2 wt%

[0110] Molding aid: beeswax 25.5 wt%

[0111] Structural stabilizer: xanthan gum 1.5 wt%

[0112] Flow modifier: talc 0.8 wt%

[0113] Water content: 0.2 wt%

[0114] Preparation method:

[0115] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix C8 alkyl glycoside, beeswax, and xanthan gum, and heat to melt at 76℃ to obtain a molten matrix.

[0116] S2. Cool the molten matrix to 39°C, add unencapsulated 5,6-dihydroxyindole and sodium isoascorbate, and mix thoroughly.

[0117] S3. Add talc powder to the mixture obtained in step S2 and mix well;

[0118] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 5MPa.

[0119] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0120] Example 6

[0121] formula:

[0122] Surfactant: Cocamidopropyl betaine 68.2 wt%

[0123] 5,6-Dihydroxyindole (sugar alcohol glassy encapsulation): 2.5 wt%

[0124] Reducing agent: Sodium thiosulfate 0.3 wt%

[0125] Molding aid: Carnauba wax 25.0 wt%

[0126] Structure stabilizer: Sodium carboxymethyl cellulose 2.5 wt%

[0127] Flow modifier: 1.2 wt% microcrystalline cellulose

[0128] Water content: 0.3 wt%

[0129] Preparation method:

[0130] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix cocamidopropyl betaine, carnauba wax, and sodium carboxymethyl cellulose, and heat to melt at 85℃ to obtain a molten matrix.

[0131] S2. Cool the molten matrix to 43°C, add the sugar alcohol glass-encapsulated 5,6-dihydroxyindole and sodium thiosulfate, and mix thoroughly.

[0132] S3. Add microcrystalline cellulose to the mixture obtained in step S2 and mix thoroughly.

[0133] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 6MPa.

[0134] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0135] Example 7

[0136] formula:

[0137] Surfactant: Sodium lauroyl glutamate 65.5 wt%

[0138] 5,6-Dihydroxyindole (lipid microcapsule encapsulation): 1.8 wt%

[0139] Reducing agent: Sodium ascorbate 3.0 wt%

[0140] Molding aid: glyceryl stearate 28.0 wt%

[0141] Structure stabilizer: 1.0 wt% hydroxypropyl methylcellulose

[0142] Flow modifier: 0.5 wt% silica

[0143] Water content: 0.2 wt%

[0144] Preparation method:

[0145] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium lauroyl glutamate, glyceryl stearate, and hydroxypropyl methylcellulose, and heat to melt at 77℃ to obtain a molten matrix.

[0146] S2. Cool the molten matrix to 40°C, add 5,6-dihydroxyindole encapsulated in lipid microcapsules and sodium ascorbate, and mix thoroughly.

[0147] S3. Add silicon dioxide to the mixture obtained in step S2 and mix thoroughly.

[0148] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 4MPa.

[0149] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0150] Example 8

[0151] formula:

[0152] Surfactant: Sodium cocoyl glycinate 69.7 wt%

[0153] 5,6-Dihydroxyindole (unencapsulated): 2.2 wt%

[0154] Reducing agent: Sodium dithionite 0.6 wt%

[0155] Molding aid: Cetyl alcohol 22.0 wt%

[0156] Structure stabilizer: Polyvinylpyrrolidone 3.0 wt%

[0157] Flow modifier: talc 2.0 wt%

[0158] Water content: 0.5 wt%

[0159] Preparation method:

[0160] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl glycinate, cetyl alcohol, and polyvinylpyrrolidone, and heat to melt at 79℃ to obtain a molten matrix.

[0161] S2. Cool the molten matrix to 44°C, add the unencapsulated 5,6-dihydroxyindole and sodium dithionite, and mix thoroughly.

[0162] S3. Add talc powder to the mixture obtained in step S2 and mix well;

[0163] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 5MPa.

[0164] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0165] Example 9

[0166] formula:

[0167] Surfactant: Sodium cocoyl methyl taurate 68.7 wt%

[0168] 5,6-Dihydroxyindole (polyol solid solution encapsulation): 0.3 wt%

[0169] Reducing agent: Sodium bisulfite 0.4 wt%

[0170] Molding aid: stearyl alcohol 27.0 wt%

[0171] Structural stabilizer: xanthan gum 2.0 wt%

[0172] Flow modifier: 1.5 wt% microcrystalline cellulose

[0173] Water content: 0.1 wt%

[0174] Preparation method:

[0175] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl methyl taurate, stearyl alcohol, and xanthan gum, and heat to melt at 81℃ to obtain a molten matrix.

[0176] S2. Cool the molten matrix to 37°C, add 5,6-dihydroxyindole and sodium bisulfite embedded in polyol solid solution, and mix evenly.

[0177] S3. Add microcrystalline cellulose to the mixture obtained in step S2 and mix thoroughly.

[0178] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 6MPa.

[0179] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0180] Example 10

[0181] formula:

[0182] Surfactant: C10 alkyl glycoside 67.0 wt%

[0183] 5,6-Dihydroxyindole (sugar alcohol glassy encapsulation): 1.2 wt%

[0184] Reducing agent: ascorbic acid 1.5 wt%

[0185] Molding aid: beeswax 17.0 wt%

[0186] Structure stabilizer: Sodium carboxymethyl cellulose 2.0 wt%

[0187] Flow modifier: 1.0 wt% silica

[0188] Water content: 0.3 wt%

[0189] Preparation method:

[0190] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix C10 alkyl glycoside, beeswax, and sodium carboxymethyl cellulose, and heat to melt at 76℃ to obtain a molten matrix.

[0191] S2. Cool the molten matrix to 41°C, add the sugar alcohol glass-encapsulated 5,6-dihydroxyindole and ascorbic acid, and mix thoroughly.

[0192] S3. Add silicon dioxide to the mixture obtained in step S2 and mix thoroughly.

[0193] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 5MPa.

[0194] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0195] Example 11

[0196] formula:

[0197] Surfactant: Sodium cocoyl hydroxyethyl sulfonate 68.0 wt%

[0198] 5,6-Dihydroxyindole (lipid microcapsule encapsulation): 0.6 wt%

[0199] Reducing agent: cysteine ​​1.5 wt%

[0200] Molding aid: Stearic acid 27.0 wt%

[0201] Structure stabilizer: 1.5 wt% hydroxypropyl methylcellulose

[0202] Flow modifier: talc 1.2 wt%

[0203] Water content: 0.2 wt%

[0204] Preparation method:

[0205] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl hydroxyethyl sulfonate, stearic acid, and hydroxypropyl methylcellulose, and heat to melt at 80℃ to obtain a molten matrix.

[0206] S2. Cool the molten matrix to 39°C, add 5,6-dihydroxyindole and cysteine ​​encapsulated in lipid microcapsules, and mix thoroughly.

[0207] S3. Add talc powder to the mixture obtained in step S2 and mix well;

[0208] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 4.5 MPa.

[0209] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0210] Example 12

[0211] formula:

[0212] Surfactant: Sodium lauroyl glutamate 72.0 wt%

[0213] 5,6-Dihydroxyindole (unencapsulated): 1.0 wt%

[0214] Reducing agent: glutathione 0.7 wt%

[0215] Molding aid: 23.1 wt% glyceryl monostearate

[0216] Structure stabilizer: Polyvinylpyrrolidone 2.0 wt%

[0217] Flow modifier: 0.8 wt% microcrystalline cellulose

[0218] Water content: 0.4 wt%

[0219] Preparation method:

[0220] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium lauroyl glutamate, glyceryl monostearate, and polyvinylpyrrolidone, and heat to melt at 78℃ to obtain a molten matrix.

[0221] S2. Cool the molten matrix to 42°C, add the unencapsulated 5,6-dihydroxyindole and glutathione, and mix thoroughly.

[0222] S3. Add microcrystalline cellulose to the mixture obtained in step S2 and mix thoroughly.

[0223] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 5MPa.

[0224] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0225] Example 13

[0226] formula:

[0227] Surfactant: Cocamidopropyl Betaine 28.0 wt%

[0228] 5,6-Dihydroxyindole (polyol solid solution encapsulation): 2.8 wt%

[0229] Reducing agent: Sodium thiosulfate 0.5 wt%

[0230] Molding aid: Carnauba wax 48.0 wt%

[0231] Structural stabilizer: xanthan gum 19.9 wt%

[0232] Flow modifier: 0.6 wt% silica

[0233] Water content: 0.2 wt%

[0234] Preparation method:

[0235] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix cocamidopropyl betaine, carnauba wax, and xanthan gum, and heat to melt at 84℃ to obtain a molten matrix.

[0236] S2. Cool the molten matrix to 43°C, add 5,6-dihydroxyindole and sodium thiosulfate embedded in polyol solid solution, and mix evenly.

[0237] S3. Add silicon dioxide to the mixture obtained in step S2 and mix thoroughly.

[0238] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 6MPa.

[0239] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0240] Example 14

[0241] formula:

[0242] Surfactant: Sodium cocoyl glycinate 52.0 wt%

[0243] 5,6-Dihydroxyindole (sugar alcohol glassy encapsulation): 1.6 wt%

[0244] Reducing agent: isoascorbic acid 1.8 wt%

[0245] Molding aid: Cetyl alcohol 28.0 wt%

[0246] Structure stabilizer: Sodium carboxymethyl cellulose 15.3 wt%

[0247] Flow modifier: talc 1.0 wt%

[0248] Water content: 0.3 wt%

[0249] Preparation method:

[0250] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl glycinate, cetyl alcohol, and sodium carboxymethyl cellulose, and heat to melt at 77℃ to obtain a molten matrix.

[0251] S2. Cool the molten matrix to 40°C, add the sugar alcohol-glass-embedded 5,6-dihydroxyindole and isoascorbic acid, and mix thoroughly.

[0252] S3. Add talc powder to the mixture obtained in step S2 and mix well;

[0253] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 5MPa.

[0254] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0255] Example 15

[0256] formula:

[0257] Surfactant: Sodium cocoyl methyl taurate 68.7 wt%

[0258] 5,6-Dihydroxyindole (lipid microcapsule encapsulation): 0.9 wt%

[0259] Reducing agent: Sodium sulfite 0.4 wt%

[0260] Molding aid: Stearyl alcohol 18.0 wt%

[0261] Structure stabilizer: 11.8 wt% hydroxypropyl methylcellulose

[0262] Flow modifier: 1.1 wt% microcrystalline cellulose

[0263] Water content: 0.1 wt%

[0264] Preparation method:

[0265] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl methyl taurate, stearyl alcohol, and hydroxypropyl methylcellulose, and heat to melt at 79℃ to obtain a molten matrix.

[0266] S2. Cool the molten matrix to 38°C, add 5,6-dihydroxyindole encapsulated in lipid microcapsules and sodium sulfite, and mix thoroughly.

[0267] S3. Add microcrystalline cellulose to the mixture obtained in step S2 and mix thoroughly.

[0268] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 4MPa.

[0269] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0270] Example 16

[0271] formula:

[0272] Surfactant: C12 alkyl glycoside 58.0 wt%

[0273] 5,6-Dihydroxyindole (unencapsulated): 2.4 wt%

[0274] Reducing agent: Sodium ascorbate 2.5 wt%

[0275] Molding aid: beeswax 13.2 wt%

[0276] Structure stabilizer: Polyvinylpyrrolidone 22.5 wt%

[0277] Flow modifier: 0.9 wt% silica

[0278] Water content: 0.5 wt%

[0279] Preparation method:

[0280] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix C12 alkyl glycoside, beeswax, and polyvinylpyrrolidone, and heat to melt at 76℃ to obtain a molten matrix.

[0281] S2. Cool the molten matrix to 44°C, add unencapsulated 5,6-dihydroxyindole and sodium ascorbate, and mix thoroughly.

[0282] S3. Add silicon dioxide to the mixture obtained in step S2 and mix thoroughly.

[0283] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 5.5 MPa.

[0284] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0285] Example 17

[0286] formula:

[0287] Surfactant: Sodium cocoyl hydroxyethyl sulfonate 62.0 wt%

[0288] 5,6-Dihydroxyindole (polyol solid solution encapsulation): 0.4 wt%

[0289] Reducing agent: Sodium dithionite 0.2 wt%

[0290] Molding aid: glyceryl stearate 24.0 wt%

[0291] Structural stabilizer: xanthan gum 12.5 wt%

[0292] Flow modifier: talc 0.7 wt%

[0293] Water content: 0.2 wt%

[0294] Preparation method:

[0295] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl hydroxyethyl sulfonate, glyceryl stearate, and xanthan gum, and heat to melt at 81℃ to obtain a molten matrix.

[0296] S2. Cool the molten matrix to 39°C, add 5,6-dihydroxyindole and sodium dithionite encapsulated in polyol solid solution, and mix thoroughly.

[0297] S3. Add talc powder to the mixture obtained in step S2 and mix well;

[0298] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 4MPa.

[0299] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0300] Example 18

[0301] formula:

[0302] Surfactant: Sodium lauroyl glutamate 56.0 wt%

[0303] 5,6-Dihydroxyindole (sugar alcohol glassy encapsulation): 1.3 wt%

[0304] Reducing agent: cysteine ​​1.1 wt%

[0305] Molding aid: Stearic acid 21.0 wt%

[0306] Structure stabilizer: Sodium carboxymethyl cellulose 19 wt%

[0307] Flow modifier: 1.3 wt% microcrystalline cellulose

[0308] Water content: 0.3 wt%

[0309] Preparation method:

[0310] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium lauroyl glutamate, stearic acid, and sodium carboxymethyl cellulose, and heat to melt at 78℃ to obtain a molten matrix.

[0311] S2. Cool the molten matrix to 41°C, add the sugar alcohol-glass-embedded 5,6-dihydroxyindole and cysteine, and mix thoroughly.

[0312] S3. Add microcrystalline cellulose to the mixture obtained in step S2 and mix thoroughly.

[0313] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 5MPa.

[0314] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0315] Example 19

[0316] formula:

[0317] Surfactant: Cocamidopropyl Betaine 54.0 wt%

[0318] 5,6-Dihydroxyindole (lipid microcapsule encapsulation): 0.7 wt%

[0319] Reducing agent: glutathione 0.6 wt%

[0320] Molding aid: 22.1 wt% glyceryl monostearate

[0321] Structure stabilizer: 22.0 wt% hydroxypropyl methylcellulose

[0322] Flow modifier: 0.4 wt% silica

[0323] Water content: 0.2 wt%

[0324] Preparation method:

[0325] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix cocamidopropyl betaine, glyceryl monostearate, and hydroxypropyl methylcellulose, and heat to melt at 80℃ to obtain a molten matrix.

[0326] S2. Cool the molten matrix to 40°C, add 5,6-dihydroxyindole and glutathione encapsulated in lipid microcapsules, and mix well.

[0327] S3. Add silicon dioxide to the mixture obtained in step S2 and mix thoroughly.

[0328] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 4.5 MPa.

[0329] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0330] Example 20

[0331] formula:

[0332] Surfactant: Sodium cocoyl glycinate 56.0 wt%

[0333] 5,6-Dihydroxyindole (unencapsulated): 1.9 wt%

[0334] Reducing agent: ascorbic acid 1.4 wt%

[0335] Molding aid: Carnauba wax 29.0 wt%

[0336] Structure stabilizer: Polyvinylpyrrolidone 9.5 wt%

[0337] Flow modifier: talc 1.8 wt%

[0338] Water content: 0.4 wt%

[0339] Preparation method:

[0340] S1. Control the moisture content of the reaction system to ≤0.3wt%. Mix sodium cocoyl glycinate, carnauba wax, and polyvinylpyrrolidone, and heat to melt at 83℃ to obtain a molten matrix.

[0341] S2. Cool the molten matrix to 42°C, add the unencapsulated 5,6-dihydroxyindole and ascorbic acid, and mix thoroughly.

[0342] S3. Add talc powder to the mixture obtained in step S2 and mix well;

[0343] S4. Place the mixture obtained in step S3 into a mold and compact it under a pressure of 6MPa.

[0344] S5. Cool to room temperature, demold, and obtain solid hair dye composition.

[0345] Performance testing:

[0346]

[0347] Analysis of test results:

[0348] The performance test results of the above embodiments show that the moisture content of all samples was strictly controlled below 0.5 wt%, which meets the design requirements of the anhydrous system of this invention. Among them, Example 15 had the lowest moisture content (0.09 wt%), providing a basic guarantee for the long-term stable storage of DHI. The pH value of the 1:99 water mixture was between 6.3 and 7.4, generally weakly acidic to neutral, indicating that the product of this invention can achieve effective dyeing without a strong alkaline environment during use and is gentle and non-irritating to the scalp. After 12 months of storage at room temperature, the DHI retention rate was generally higher than 90%. Among them, Examples 2, 3, 6, and 13, which used the embedding technology, all had retention rates exceeding 96%, while Examples 8 and 16, which were not embedded or had higher moisture content, had relatively lower retention rates, but still remained above 88.5%. This fully verifies the significant improvement effect of the multiple synergistic mechanism of "anhydrous system + reducing agent protection + structural densification + oxygen-barrier encapsulation" on the stability of DHI. In addition, the hair strength retention rate after dyeing is above 97%, and in Examples 3, 7 and 15 it is close to 99%, indicating that the product of the present invention can effectively dye hair black while causing almost no damage to the hair keratin structure, which is significantly better than traditional oxidative hair dyes.

[0349] The performance of the hair dye composition prepared in Example 9 was tested, and the results are as follows:

[0350] The solid hair dye composition prepared in this embodiment has a moisture content of 0.12 wt%, a pH value of 6.4 after mixing with water at a ratio of 1:99, and a 5,6-dihydroxyindole (DHI) activity retention rate of 93.6% after 12 months of sealed storage at room temperature, and a hair strength retention rate of 98.8% after dyeing.

[0351] Hair dyeing effect test:

[0352] like Figure 1 As shown, using Example 1 as the test material and white wool as the test substrate, the dyeing effect test was conducted by simulating the human hair dyeing process. The specific dyeing method was as follows: the white wool was moistened with water at room temperature, the solid hair dyeing composition of this example was applied to the surface of the moistened white wool, left to stand naturally for 5 minutes, then rinsed with water, and placed in a ventilated place to dry, thus completing one dyeing operation.

[0353] Results of multiple dyeing processes: After the first to fourth dyeing, the white wool showed good dyeing results, presenting a uniform natural black tone; from the fifth to the fourteenth dyeing stage, the wool color remained stable, with no obvious fading or graying; after the fifteenth dyeing, the wool color turned grayish-black, and the color saturation was slightly lower than the previous dyeing.

[0354] Gray hair coverage rate: After multiple tests and statistics, the composition of this embodiment has a moderate coverage rate for white wool, with an average coverage rate of about 90%.

[0355] Results analysis:

[0356] This embodiment achieves efficient and stable storage of 5,6-dihydroxyindole through polyol solid solution encapsulation, combined with an anhydrous system and the reducing microenvironment protection provided by sodium bisulfite, resulting in an activity retention rate of 93.6% after 12 months and a hair strength retention rate of nearly 99% after dyeing, demonstrating excellent hair-friendly properties. Regarding the dyeing effect, multiple initial dyeing sessions achieve a good natural black color, with only the fifteenth dyeing session resulting in a grayish hue. The coverage rate for gray hair reaches 90%, and the overall dyeing effect meets the application requirements of solid hair dye compositions, verifying the feasibility of the formulation and preparation method of this invention.

[0357] In summary, this invention successfully solves the technical challenge of easy oxidation and inactivation of 5,6-dihydroxyindole during storage by constructing an anhydrous solid system, introducing a reducing agent for protection, and combining various encapsulation techniques and structural densification processes. It achieves an activity retention rate of over 97% after long-term stable storage at room temperature, eliminates the need for strong alkalis and strong oxidants in the hair dyeing process, and maintains nearly 99% of the hair strength after dyeing, exhibiting high safety, high stability, and high dyeing effect. This solid hair dye composition is morphologically stable, requires no preservatives, is easy to carry and use, and has a simple preparation process with controllable temperature, demonstrating good feasibility for industrial production. Based on its natural melanin precursor structure, mild hair dyeing mechanism, and excellent application performance, this invention has broad market application prospects in the personal care and hair dyeing product fields, especially suitable for consumers seeking a safe, environmentally friendly, and mild hair dyeing experience, and is expected to drive the upgrading and development of hair dyeing products towards green, low-irritation, and highly biocompatible directions.

[0358] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A solid hair dye composition based on 5,6-dihydroxyindole, characterized in that, By mass percentage, it includes the following components: 5,6-Dihydroxyindole 0.1–3.0 wt% Reducing agent 0.05–5.0 wt% Surfactant 10.0–75.0 wt% Molding aids 10.0–50.0 wt% Structural stabilizer 0.5–30.0 wt% Flow modifier 0–5.0 wt% The remainder is water. in: a) The composition has a solid molded structure and its moisture content is not higher than 0.5 wt%; b) The 5,6-dihydroxyindole exists in the solid molded structure in an embedded and / or unembedded form; c) The reducing agent and the 5,6-dihydroxyindole form a locally reducing microenvironment in the solid molded structure, thereby inhibiting the oxidative polymerization reaction of 5,6-dihydroxyindole under storage conditions, so that after the composition is sealed and stored at room temperature for 12 months, the activity retention rate of 5,6-dihydroxyindole is not less than 90%.

2. The solid hair dye composition based on 5,6-dihydroxyindole according to claim 1, characterized in that, The surfactants include sodium lauroyl glutamate, sodium cocoyl glycinate, sodium cocoyl methyl taurate, sodium cocoyl hydroxyethyl sulfonate, cocamidopropyl betaine, and / or C8-C16 alkyl glycosides.

3. The solid hair dye composition based on 5,6-dihydroxyindole according to claim 1, characterized in that, The reducing agent includes ascorbic acid, sodium ascorbate, isoascorbic acid and its salts, sulfites, bisulfites, dithionites, thiosulfates, cysteine, or glutathione.

4. The solid hair dye composition based on 5,6-dihydroxyindole according to claim 1, characterized in that, The molding aids include cetyl alcohol, stearyl alcohol, stearic acid, glyceryl stearate, glyceryl monostearate, beeswax, or carnauba wax.

5. A solid hair dye composition based on 5,6-dihydroxyindole according to claim 1, characterized in that, The structural stabilizers include xanthan gum, sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, or polyvinylpyrrolidone.

6. A solid hair dye composition based on 5,6-dihydroxyindole according to claim 1, characterized in that, The flow modifier includes silica, talc, or microcrystalline cellulose.

7. A method for preparing a solid hair dye composition based on 5,6-dihydroxyindole as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Control the moisture content of the reaction system. Under anhydrous or low-moisture conditions, mix and melt the surfactant, molding aid, and structural stabilizer to obtain a molten matrix. S2. Cool the molten matrix to a suitable temperature, add embedded or unembedded 5,6-dihydroxyindole and a reducing agent, and mix thoroughly. S3. Add the flow modifier to the mixture obtained in step S2 and mix thoroughly; S4. Place the mixture obtained in step S3 into a mold and compact it under a certain pressure; S5. Cool and demold to obtain a solid hair dye composition.

8. The method for preparing a solid hair dye composition based on 5,6-dihydroxyindole according to claim 7, characterized in that, In step S1, the moisture content of the reaction system is ≤0.3wt%.

9. A method for preparing a solid hair dye composition based on 5,6-dihydroxyindole according to claim 7, characterized in that, In step S2, the suitable temperature after the molten matrix is ​​cooled is no higher than 45°C.

10. A method for preparing a solid hair dye composition based on 5,6-dihydroxyindole according to claim 7, characterized in that, The 5,6-dihydroxyindole is present in an encapsulated form, wherein the encapsulation method is at least one of the following: (1) Glassy embedding of sugar alcohols: 5,6-dihydroxyindole is dissolved in erythritol and / or sorbitol system and dried under reduced pressure to form a glassy solid; (2) Lipid microcapsule encapsulation: using beeswax and / or fatty acid glycerides as wall materials, 5,6-dihydroxyindole is encapsulated to form microcapsules by melt dispersion method; (3) Polyol solid solution embedding: 5,6-dihydroxyindole is formed into a solid solution in anhydrous glycerol or propylene glycol.

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