Hair dyeing method

Abstract

The present invention relates to a cosmetic hair dyeing method comprising the steps of: (a) applying to at least one strand of hair an aqueous dyeing composition comprising one or more ionic direct dyes; and (b) exposing the hair impregnated with the dyeing composition to microwave radiation.

Description

[Technical Field]

[0001] The present invention relates to a method for dyeing hair. [Background technology]

[0002] Numerous techniques have already been proposed for dyeing hair, using different types of dye compositions.

[0003] Additionally, in the field of surface repair, it is known to use microwave radiation to increase the action of cleaning agents. In particular, applications WO 98 / 03621, WO 98 / 03622, WO 98 / 03623, WO 99 / 25802 and WO 99 / 37745 describe hard surface treatments in which exposure to microwave radiation is combined with cleaning agents containing bleach.

[0004] In the field of hair shaping, applications DE3148538, US2006 / 0108358, US2010 / 0006116 or US2007 / 056860 disclose the use of microwave radiation directly on the hair.

[0005] Documents US2006 / 042649 and US6079422 describe heated curlers that can be placed in a microwave oven before being used to curl the hair. In these documents, it is the heat-generating aspect of microwaves that is used, but these microwaves do not come into direct contact with the hair.

[0006] Application WO2013 / 183021 discloses a method for the treatment of keratinous fibers, which comprises the application of a molding composition followed by the application of mechanical tension and then exposure to microwave radiation.

[0007] Applications WO2011 / 141882 and FR3062786 describe a method for treating hair by subjecting it to mechanical tension and exposing it to microwave radiation.

[0008] Application WO2013 / 125052 describes a method for coloring hair using synthetic direct dyes and heating of keratin fibers.

[0009] Application WO2019 / 122850 discloses a method for dyeing hair using a dyeing composition and simultaneous treatment with radio-wave radiation having a frequency between 1 MHz and 300 MHz.

[0010] Shaping the hair and dyeing this same hair usually require two different operations, which, on the one hand, result in long cumulative waiting times and, on the other hand, a significant increase in the risk of altering the color obtained on the hair and even damaging the keratin fibers, making immediate successive application undesirable. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] WO98 / 03621 [Patent Document 2] WO98 / 03622 [Patent Document 3] WO98 / 03623 [Patent Document 4] WO99 / 25802 [Patent Document 5] WO99 / 37745 [Patent Document 6] DE3148538 [Patent Document 7] US2006 / 0108358 [Patent Document 8] US2010 / 0006116 [Patent Document 9] US2007 / 056860 [Patent Document 10] US2006 / 042649 [Patent Document 11] US6079422 [Patent Document 12] WO2013 / 183021 [Patent Document 13] WO2011 / 141882 [Patent Document 14] FR3062786 [Patent Document 15] WO2013 / 125052 [Patent Document 16] WO2019 / 122850 Summary of the Invention [Problem to be solved by the invention]

[0012] As a result, there remains a need to improve hair dyeing methods by preserving the hair fiber as much as possible while increasing their effectiveness, in particular to provide more effective direct dyeings with enhanced color strength and / or reduced selectivity and / or improved durability, especially with respect to shampooing.

[0013] There is also a need to propose a method for simultaneously dyeing and shaping hair. [Means for solving the problem]

[0014] Dyeing method The present invention aims to meet this need and the subject matter of the invention comprises at least (a) applying an aqueous dye composition comprising one or more ionic direct dyes to at least one strand of hair; (b) exposing the hair impregnated with the dyeing composition to microwave radiation; The cosmetic hair dyeing method includes the steps of:

[0015] The method according to the invention makes it possible to obtain an improved hair dyeing treatment by means of a specific combination of ionic direct dyes and microwave radiation. The use of microwave radiation while the dyeing composition is still present on the hair results in targeted excitation of the molecules, making it possible to reduce the exposure time to obtain comparable results.

[0016] It is also possible to reduce the concentration of ionic direct dye used to achieve a given level of coloration.

[0017] The dyeing results are very good, in particular good dye deposition, good durability and low selectivity, whilst causing limited damage to the hair.

[0018] It is also possible to use compositions having a lower pH than that of known dye compositions.

[0019] The use of microwave radiation makes it possible to accelerate the dyeing reaction and therefore reduce the standing time required for the composition.

[0020] The durability and uniformity of the results obtained from the method according to the invention are very good, the hair experiences less damage and the risk of irritation is limited.

[0021] Depending on the duration of exposure to microwave radiation, and especially depending on the base color of the hair strand, different results are obtained.

[0022] The duration of exposure to microwave radiation may range from 1 second to 30 minutes, even better from 1 second to 10 minutes, even better from 1 second to 5 minutes, and very preferentially from 1 second to 3 minutes.

[0023] The method according to the invention may further comprise a hair shaping step (d) comprising applying mechanical tension to said strand of hair, in particular via a device for applying mechanical tension having a receiving surface intended in particular to receive said strand of hair, in particular a step of winding the strand of hair on curlers.

[0024] The method according to the invention can therefore contribute in parallel to the degree of shaping of the hair and offers the possibility of carrying out the dyeing and shaping process simultaneously in a long-lasting, fast and satisfactory manner: the curls are well defined, sufficiently durable and the damage is limited.

[0025] In this variation, the shaping step (d) can be carried out before step (a) of applying the composition or between step (a) and step (b) of exposing to microwave radiation.

[0026] The method according to the invention may optionally further comprise one or more pretreatment steps carried out before steps (a) and (b) and / or before or after step (d).

[0027] The method according to the invention may optionally further comprise one or more post-treatment steps carried out after step (b) and / or after step (c).

[0028] These further pre- or post-treatment steps may include applying one or more further compositions other than those present in step (a), which may or may not be followed immediately by microwave treatment.

[0029] When shaping step (d) is carried out, the method according to the invention may also comprise a step (e) of applying a hair shaping composition comprising one or more fixing polymers or one or more agents that disrupt the disulfide bonds of keratin, such as a thiol-containing reducing agent. Preferably, the method according to the invention does not comprise such a step (e).

[0030] The method according to the present invention may further comprise one or more steps (c) of rinsing the hair after any of steps (a), (b) and (d), preferably a single rinsing step carried out after step (b) of exposure to microwave radiation.

[0031] composition The dyeing composition preferably comprises at least 5% by weight of water at room temperature (25° C.) and atmospheric pressure (760 mm of mercury).

[0032] The dyeing composition can be obtained from a mixture of several compositions, in particular a mixture of a composition (a1*) comprising one or more ionic direct dyes and an aqueous composition (a1**) comprising, in particular, at least one oxidizing agent. The aqueous composition (a1**) can itself be obtained from the mixture of two or more compositions. The mixture of the compositions is preferably carried out at the time of use of the dyeing composition.

[0033] The dyeing composition (a1) may comprise at least one oxidizing agent.

[0034] Composition (a1) may contain hydrogen peroxide. This hydrogen peroxide may be derived from an anhydrous hydrogen peroxide precursor, such as urea peroxide, which is then present in the composition, and which hydrolyzes directly in composition (a1**) or in composition (a1). More preferentially, the hydrogen peroxide may be in the form of an aqueous hydrogen peroxide solution present in composition (a1**).

[0035] In one variant, composition (a1) does not contain an oxidizing agent. In this variant, the method according to the invention may comprise a step (f) of applying an oxidizing composition after step (b), said oxidizing composition then preferably containing hydrogen peroxide in an aqueous medium. Preferably, the method according to the invention does not comprise this step (f).

[0036] Preferably, the dye composition (a1) has a pH ranging from 1 to 13, even better from 1.5 to 12 and even better still from 2.5 to 11.

[0037] The dyeing composition (a1) may comprise one or more pH agents, which may be alkaline or acidic.

[0038] Preferably, composition (a1) comprises one or more direct acid dyes, which also comprise one or more acid pH agents.

[0039] Preferably, composition (a1) comprises one or more direct basic dyes, which also comprise one or more alkaline pH agents.

[0040] An agent is considered alkaline if, at room temperature and atmospheric pressure, it is introduced into water at a mass concentration of 1% and produces a pH greater than 7. An agent is considered acidic if, at room temperature and atmospheric pressure, it is introduced into water at a mass concentration of 1% and produces a pH less than 7.

[0041] The alkaline agent is preferably selected from alkali metal or alkaline earth metal hydroxides, alkali metal or alkaline earth metal carbonates, ammonia and alkanolamines, among which monoethanolamine is preferred.

[0042] The acid agent is preferably selected from mineral acids, such as hydrochloric acid or phosphoric acid, organic acids, and especially hydroxy acids, such as citric acid or lactic acid.

[0043] The concentration of the pH agent in the dye composition (a1) preferably varies from 0.01% to 20% by weight, better still from 0.01% to 10%, and even better still from 0.1% to 5% by weight relative to the total weight of the composition.

[0044] The dye composition (a1) comprises one or more ionic direct dyes. By ionic direct dyes is meant dyes that have one or more permanent positive or negative charges. Ionic direct dyes can be anionic or cationic. They are in particular direct "acid" dyes and direct "basic" dyes.

[0045] Direct "acid" dyes have at least one chlorinated or unchlorinated sulfonic or carboxylic acid group in their structure. Direct "basic" dyes have at least one quaternized nitrogen atom in the presence of at least one counterion in their structure.

[0046] As direct acid dyes, mention may be made of the dyes listed in the Color Index under the names Acid Yellow 1, Acid Orange 3, Acid Black 1, Acid Black 52, Acid Orange 7, Acid Red 33, Acid Yellow 23, Acid Blue 9, Acid Violet 43, Acid Blue 62, Acid Blue 25, Acid Red 4.

[0047] As basic dyes, mention may be made of the dyes listed in the Colour Index under the names Basic Brown 17, Basic Red 118, Basic Orange 69, Basic Red 76, Basic Brown 16, Basic Yellow 57, Basic Violet 14, Basic Blue 7, Basic Blue 26, Basic Red 2, Basic Blue 99, Basic Yellow 29, Basic Red 51, Basic Orange 31, Basic Yellow 87, Basic Blue 124.

[0048] In the dye composition (a1), the concentration of the ionic direct dye may vary from 0.001% to 20% by weight, better still from 0.01% to 15% by weight, and even better still from 0.1% to 10% by weight relative to the total weight of the composition.

[0049] The cosmetic composition used in the method according to the invention may also comprise at least one compound selected from solvents, silicone or non-silicone fatty substances, silicone or non-silicone anionic, cationic, non-ionic or amphoteric surfactants, polymers and in particular anionic, cationic, non-ionic or amphoteric treating or thickening polymers, antidandruff agents or agents to prevent hair loss.

[0050] microwave radiation The term "microwave" should be understood to mean electromagnetic radiation having a frequency in the range of 500 MHz to 300 GHz.

[0051] Preferably, the frequency of the microwave radiation used in the method of the invention is in the range from 500 MHz to 300 GHz, even better from 500 MHz to 10 GHz, even better from 900 MHz to 5 GHz, and very preferentially from 2 GHz to 3 GHz.

[0052] The microwave power used during step (b) may be in the range of 500W or less, preferably 10-300W, even better 100-250W, even better still 10-50W.

[0053] Preferably, the surface power density at the hair induced by microwave radiation is less than 0.1 W / cm 2 ~100W / cm 2 The range can be:

[0054] The exposure to microwave radiation may be carried out by means of a microwave-emitting antenna, said antenna and at least a portion of the lock to be treated being inserted in an enclosure that is preferably leak-tight to microwaves.

[0055] Optionally, at least during step (b), the housing contains the hair to be treated, which is impregnated with the dye composition. The term "containing hair" should be understood to mean containing the hair over a given width, over the entire length or a portion of the length. The housing may cover the hair over a length of, for example, 5 cm or more. Thus, hair of at least 5 cm in length can be treated in the housing at one time.

[0056] The enclosure may be defined at least in part by a case having a housing configured to receive at least a portion of the hair to be treated and optionally a hair shaping tool, and by a cover that rotates relative to the case between an open position and a closed position to provide access to the housing, the microwave emitting antenna being located inside the housing.

[0057] In one variant, the housing is in the form of a hood.

[0058] The housing may be stationary relative to the treated hair during microwave emission or may be movable relative to the hair, allowing longer lengths of hair to be treated.

[0059] The housing may comprise at least one seal, for example of an elastically deformable electrically conductive material, which allows the hair to exit the housing while shielding the microwaves used in step (b). The seal may comprise a foam filled with electrically conductive particles, a brush formed of electrically conductive bristles, or a comb with metal teeth.

[0060] If the housing is in the form of a hood, it may have an electromagnetic shielding through which the treated hair may pass. Such shielding makes it possible to protect the user's head from the emitted microwaves while treating the user's hair. The electromagnetic shielding may be formed, for example, by a metal grid or mesh.

[0061] assembly According to another of its aspects, another subject of the invention is an assembly for dyeing hair, comprising at least one dyeing composition containing one or more ionic direct dyes and a device suitable for exposing the hair to microwave radiation as previously defined.

[0062] The device may comprise a microwave-emitting antenna, the antenna and at least a part of the bunch to be treated being inserted into a microwave-tight enclosure, in particular as described above.

[0063] The microwaves may be generated internally within the device suitable for exposing the hair to microwave radiation, or externally by a microwave generator, for example a solid state generator, such as a magnetron.

[0064] In one variation, the oscillator is located inside the housing.

[0065] The microwave emission can be carried out, for example, by a non-linear antenna of the helical type.

[0066] The antenna may be formed of a sufficiently rigid wire, for example with a diameter in the range of 1 to 3 mm, so as not to require a support rod for maintenance or rotation. Alternatively, the antenna comprises a flexible wire or a conductive track arranged on a support structure, in particular a helical support structure. This support structure may be made of any insulating material, preferably PTFE or glass.

[0067] If helical, the antenna preferably has a fixed helical pitch, for example in the range of 4 to 5 mm. The radius of the helix is ​​preferably constant, for example in the range of 4 to 10 mm. The diameter of the antenna is, for example, 8 to 10 mm.

[0068] The axial extension of the antenna may vary from 50 to 80 mm, and even better from 65 to 75 mm.

[0069] The antenna may in particular be arranged in a tube closed at one end, which may be made of PTFE or another insulating material.

[0070] The antenna may also be embedded in an insulating material, preferably a flexible insulating material, especially silicone.

[0071] Said device suitable for exposing hair to microwave radiation may comprise a hair shaping tool, in particular a tool for applying mechanical tension, in particular a curler. The term "curler" denotes a tool that makes it possible to wind the hair along the longitudinal axis of the device according to a predetermined diameter, thereby creating a diameter-based mechanical tension. The diameter of said curler may depend on the desired curling effect.

[0072] The curler may have teeth at the end of the arms that laterally delimit the hair receiving surface, said teeth of the curler being advantageously arranged around the antenna.

[0073] The shaping tool may optionally be configured to flatten the treated hair during microwave exposure.

[0074] The removal of mechanical tension on said strand of hair is preferably carried out after step (b) of exposure to microwave radiation.

[0075] The device may comprise a housing capable of receiving a shaping tool, said housing being coated with a conductive foam arranged to overflow into the hair exit slot, thereby making it possible to obtain good leaktightness of the enclosure due to the deformability of the foam in the slot.

[0076] Optionally, the moulding tool and the antenna form an integral assembly that is installed in the housing.

[0077] The moulding tool may be made of PTFE or other insulating material, especially a thermoplastic insulating material.

[0078] The device used to carry out the method according to the invention may be equipped with an audible and / or optical warning system to warn the user of, for example, microwave leakage from the enclosure and / or excessively high temperatures inside the enclosure.

[0079] The device advantageously comprises a safety system that prevents microwave emission while the enclosure is not closed and / or in the event of abnormal operation, for example in the event of microwave leakage and / or excessively high temperatures.

[0080] The device may be configured to control the duration of microwave emission so as not to reach a treatment duration that is likely to damage the hair.

[0081] The method according to the invention may comprise, before step (b), a step of detecting closure of the housing, for example, activating a contactor when the housing is closed.

[0082] Initiation of microwave emission may depend on detection of closure of the enclosure. After initiation of microwave emission, continued microwave emission may depend on no microwave leakage being detected by a sensor located outside the enclosure that is specifically sensitive to microwaves.

[0083] The method according to the invention may further comprise, before step (b), a step of detecting the position of the hair intended to be treated. This detection step can be carried out, for example, by means of an optical sensor and / or a mechanical sensor. Optionally, the detection can be carried out indirectly by detecting the position of a shaping tool.

[0084] The method according to the invention may, for example, comprise a step of measuring the temperature to which the treated hair is subjected during step (b). This step of measuring the temperature can be carried out by means of a thermometer, without contact with the hair.

[0085] The device may comprise a microwave generator and also a shaping tool in one and the same handpiece. The term "handpiece" denotes the part that the user operates with one hand while treating the hair.

[0086] The device may be equipped with sensors that sense individual hair characteristics, such as color, mechanical strength, surface condition or humidity, and the device can appropriately control at least one parameter of the treatment, such as microwave energy, solvent temperature, duration of treatment and / or applied mechanical stress, based on the characteristics thus detected.

[0087] The features given above for the method apply to the assembly and vice versa.

[0088] A better understanding of the invention will be obtained from reading the following description and examining the accompanying drawings, which are presented purely by way of example and without limiting the invention in any way. [Brief explanation of the drawings]

[0089] [Figure 1] 1 illustrates the various steps of an example hair dyeing method according to the present invention. [Figure 2] 1 shows a schematic and partial view of an example of a device suitable for carrying out the method according to the invention; [Figure 3] 1 shows a handpiece of an example of a device suitable for carrying out a method according to the invention in an open position. [Figure 4] FIG. 4 shows the handpiece of FIG. 3 in a closed position. [Figure 5] FIG. 1 shows a shaping tool extracted from the handpiece of a variant of a device suitable for carrying out the method according to the invention. [Figure 6] 6 is a cross-sectional side view of a device with the molding tool of FIG. 5 suitable for carrying out the method according to the invention when the housing is closed. DETAILED DESCRIPTION OF THE INVENTION

[0090] The various steps of an example of a hair dyeing method according to the present invention are shown in FIG. 1 and are described in detail below.

[0091] In this example, in step 11, an aqueous dye composition (a1) comprising one or more ionic direct dyes is applied to at least one strand of hair.

[0092] In step 12, the hair contacted with the dyeing composition is exposed to microwave radiation having a frequency of 500 MHz or higher, preferably in the range of 900 MHz to 5 GHz. The duration of exposure to microwave radiation is preferably in the range of 1 second to 3 minutes. The surface power density at the hair induced by the microwave radiation is 0.1 W / cm. 2 ~100W / cm 2 The range can be:

[0093] The method according to the invention further comprises, in the example described, one or more rinsing steps 13, preferably a single hair rinsing step 13, carried out after step 12 after exposure to microwave radiation.

[0094] The method according to the invention may further comprise a hair shaping step 14, in particular a step of winding the hair strand on curlers, which comprises applying mechanical tension to said at least one strand of hair via a device for applying mechanical tension having a receiving surface intended to receive said strand of hair. This shaping step 14 is carried out before step 11 of applying the dye composition or between steps 11 and 12.

[0095] The method according to the invention may further comprise one or more pre-treatment steps 15 carried out before steps 11 and 12, for example comprising applying one or more additional compositions other than those used during step 11.

[0096] For example, one or more post-treatment steps 16, including applying one or more additional compositions other than those used in step 11, may be performed after step 12 and / or after step 13.

[0097] Preferably, as in the described example, the dyeing composition (a1) may be a mixture of several compositions, in the example in question being a mixture of a composition (a1*) comprising one or more ionic direct dyes and an aqueous composition (a1**) comprising hydrogen peroxide, the mixing of the compositions being carried out at the time of use of the dyeing composition. The dyeing composition (a1), the pH of the ionic direct dye(s) and optional pH agent(s) contained in the dyeing composition (a1), and their concentrations are as described above.

[0098] 2 shows a device 100 suitable for carrying out the method according to the invention, comprising a handpiece 3 connected by a flexible waveguide 2 to a base unit 1 comprising a microwave generator. The handpiece 3 is adapted to be operated by a user for placement adjacent to a person's head for treating at least one strand of hair H, as shown. The handpiece 3 can be made in various ways and defines a treatment enclosure 4 which is leak-tight to microwaves.

[0099] In the example shown in Figure 3, the handpiece 3 comprises a case 10 defining a housing 6, onto which a cover 11 is connected by a pin 12. In Figure 4 the handpiece is shown in a closed state. The flexible waveguide 2 is only very partially shown in Figures 3 and below.

[0100] The case 10 carries an antenna 30, which in the example shown is of a spiral shape with a longitudinal axis Y.

[0101] In the example in question, the antenna 30 consists of a spiral metal wire disposed in a tube 32 of insulating material, such as silicone or PTFE.

[0102] The antenna 30 is supported at one axial end of the case 10 by an end plate 14 of the case 10, which has a semicircular outer shape.

[0103] The cover 11 has a similar end plate 15 on the opposite side to close the opening 5 in the housing 6 through which a molding tool can be introduced into the handpiece 3 .

[0104] The inner surface of the housing 6 is defined by an electrically conductive coating 7, which makes it possible to reflect microwaves and makes the enclosure 4 leakproof to microwaves. This coating 7 can be made of conductive foam, for example in the form of a semi-cylindrical shape, for the cover and case in the form of a disk for the end plate 15 and a ring for the end plate 14.

[0105] The case 10 and cover 11 define a hair exit slot 19 located at the bottom of the recess 18 opposite the hinge pin 12.

[0106] The coating 7 preferably protrudes into the slot 19, as can be seen in Figure 6, to produce good leaktightness of the housing despite the passage of hair. Thus, at 17, the edge of the coating can extend slightly beyond the edge of the body of the cover and the edge of the case, closing off the slot 19.

[0107] The handpiece 3 is provided with a member (not shown) for fixing the cover in the closed position and / or an open detector.

[0108] A temperature detector may be present inside the housing 4, e.g., on the inner surface of the housing, to measure the temperature of the treated hair strand, and a control system, e.g., having a microprocessor, may be able to interrupt or adjust the emission of microwaves if the detected temperature exceeds a predetermined threshold.

[0109] In a particular embodiment, the case 10 defines a housing 6 for receiving a forming tool, which in the example in question consists of a curler 20, shown in Figure 5. The presence of a tube 32, shown in Figure 3, in which the wires of the antenna 30 are arranged, facilitates the insertion of the antenna inside the curler 20.

[0110] The curler comprises several arms 21 which define a surface for receiving hair H, of width L measured along the longitudinal axis X of the curler 20 .

[0111] In this example, axis X is parallel to the axis of rotation of cover 11 and coincides with longitudinal axis Y of antenna 30 .

[0112] In the example in question, the curler 20 comprises four arms 21, which are slightly curved towards the axis X and have their shortest distance to the axis X approximately in the middle of their length.

[0113] Arm 21 may have ribs 23 oriented perpendicular to axis X to help keep the tufts spread across arm 21, preferably occupying the entire width L as evenly as possible.

[0114] The arm 21 is connected at its end to a loop portion 25 .

[0115] The curler 20 has teeth 26 at the end of the arms 21 which laterally delimit a surface for receiving hair.

[0116] The curler 20 can be made of any insulating material, preferably PTFE.

[0117] The curler 20 preferably has a shape of revolution that is symmetrical about a central plane of symmetry perpendicular to the axis X.

[0118] The curler 20 is provided with studs 27 with enlarged heads to keep the curler centered in the housing 6, as shown in FIG. 6, which are connected at their bases to corresponding annular portions 25 and supported on the coating 7.

[0119] Studs 27 are positioned, for example, between teeth 26 as shown.

[0120] The width W of the hair exit slot 19 may be slightly greater than the length L of the housing 6, which is substantially equal to the length of the curler 20, so that the curler is fixed both axially and radially to the housing 6, leaving a small amount of play.

[0121] To use the handpiece 3, a strand of hair impregnated with the dye composition is wound on the curlers 20, which are then placed inside said case 10 by moving them laterally relative to said case and introducing them through the opening 5. The cover 11 is then closed again and the hair exits through the slot 19. Once the exposure to microwaves has been carried out, the strand of hair is extracted by carrying out the operation in reverse. [Example]

[0122] Examples of results obtained with the method according to the invention are summarized in table 4 below.

[0123] In this example, the color test was carried out on Caucasian sensitized hair of type SA50.

[0124] The composition used in this example according to the invention is a dyeing composition (a1) containing the cationic direct dye Basic Blue 99 (C1), which is compared with another dyeing composition not encompassed by the invention, containing the nonionic direct dye HC Blue 14 (C2). Both of these dyeing compositions produce blue shades.

[0125] The composition is as follows:

[0126] [Table 1]

[0127] [Table 2]

[0128] [Table 3]

[0129] The two dye compositions were applied to both sides of the hair tress using a brush, and the impregnated strands were then exposed to microwave radiation for 3 minutes at a power setting of 100 W.

[0130] The observed color parameters are L, a, b, and ΔE. The ΔE parameter corresponds to a measurement of the change in visual perception of two given colors before and after treatment with the method of the present invention, and is equivalent to the increase in color tint.

[0131] The results obtained by carrying out the method according to the invention are compared with those obtained by carrying out a state-of-the-art dyeing method without microwave radiation, in which the hair impregnated with the dyeing composition is heated to 90°C for 3 minutes.

[0132] [Table 4]

[0133] Compared to the state of the art method, the color gain is higher for cationic direct dye C1 when microwaves are used. However, for nonionic direct dye C2, the color gain is significantly reduced by the use of microwaves.

[0134] Many modifications can be made to the methods and devices as described without departing from the scope of the invention.

[0135] The present invention is not limited to any particular type of forming tool or any particular type of microwave emitting antenna. [Explanation of symbols]

[0136] 1 base unit 2 Flexible waveguide 3 Handpieces 4. Cabinet 5 Opening 6. Housing 7. Electrically conductive coating 10 cases 11 Cover 12-pin 14, 15 End plates 18 Recess 19 Exit Slot 20 curlers 21 Arm 23 Ribs 25 Annular section 26 teeth 27 studs 30 Antenna 32 tube 100 devices

Claims

1. at least (a) applying to at least one strand of hair an aqueous dye composition (a1) comprising one or more ionic direct dyes; (b) exposing the hair impregnated with the dyeing composition to microwave radiation; A cosmetic hair dyeing method comprising the steps of:

2. 2. The method according to claim 1, wherein the frequency of the microwave radiation used in the method of the invention is in the range from 500 MHz to 300 GHz, even better from 500 MHz to 10 GHz, even better from 900 MHz to 5 GHz, and very preferentially from 2 GHz to 3 GHz.

3. 3. The method according to claim 1 or 2, further comprising a hair shaping step (d) comprising applying mechanical tension to said at least one strand of hair, in particular via a device for applying mechanical tension having a receiving surface intended to receive said strand of hair, in particular a step of winding said strand of hair on curlers, wherein the shaping step (d) is preferably carried out before step (a) of applying the composition or between step (a) and step (b) of exposing to microwave radiation.

4. 4. The method according to claim 1, wherein the dyeing composition (a1) is obtained from a mixture of several compositions, in particular a mixture of a composition (a1*) comprising one or more ionic direct dyes and an aqueous composition (a1**) comprising in particular at least one oxidizing agent, the mixing of the compositions being carried out in particular at the time of use of the dyeing composition.

5. 5. The method according to claim 1, wherein the dyeing composition (a1) comprises at least one oxidizing agent.

6. 6. The method according to claim 5, wherein the dye composition (a1) comprises hydrogen peroxide, in particular in the form of an aqueous hydrogen peroxide solution present in the composition (a1**).

7. 5. The method according to claim 1, wherein the dyeing composition (a1) is free of oxidizing agents.

8. 8. The method according to claim 1, wherein the dyeing composition (a1) has a pH ranging from 1 to 13, even better from 1.5 to 12, and even better from 2.5 to 11.

9. 9. The method according to claim 1, wherein the dyeing composition (a1) comprises one or more pH agents, in particular alkaline or acidic agents.

10. 10. The method according to claim 9, wherein in the dye composition (a1), the concentration of pH agent varies from 0.01% to 20% by weight, better still from 0.01% to 10% by weight, and even better still from 0.1% to 5% by weight relative to the total weight of the composition.

11. 11. The method according to claim 1, wherein in the dye composition (a1) the concentration of ionic direct dye(s) varies from 0.001% to 20% by weight, better still from 0.01% to 15% by weight, and even better still from 0.1% to 10% by weight relative to the total weight of the composition.

12. 12. The method according to any one of claims 1 to 11, wherein the exposure to microwave radiation is carried out by means of a microwave-emitting antenna, said antenna and at least a part of the lock to be treated being inserted in a microwave-tight enclosure.

13. The surface power density at the hair induced by microwave radiation is 0.1 W / cm 2 ~100W / cm 2 13. The method according to any one of claims 1 to 12, wherein the range is

14. 14. The method according to any one of claims 1 to 13, wherein the duration of exposure to microwave radiation ranges from 1 second to 30 minutes, even better from 1 second to 10 minutes, even better from 1 second to 5 minutes, and very preferentially from 1 second to 3 minutes.

15. Assembly for dyeing hair, comprising at least one dyeing composition containing one or more ionic direct dyes and a device suitable for exposing the hair to microwave radiation having a frequency in the range from 500 MHz to 300 GHz, even better from 500 MHz to 10 GHz, even better from 900 MHz to 5 GHz, and very preferentially from 2 GHz to 3 GHz.

16. 16. An assembly according to claim 15, wherein the device comprises a microwave-emitting antenna (30), said antenna and at least a part of the bunch to be treated being inserted into a microwave-tight enclosure (4).

17. 17. An assembly according to claim 15 or 16, wherein the device comprises a hair shaping tool, in particular a tool for applying mechanical tension, in particular a curler.

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