Hair coloring process

Abstract

Hair coloring process. The invention relates to a cosmetic hair coloring process comprising at least the steps of: a) applying to at least one strand of hair an aqueous coloring composition comprising one or more oxidizing dyes and one or more nitrogenous alkali agents, b) exposing the hair impregnated with the coloring composition to microwave radiation. Figure for the abstract: Fig 1.

Description

Title of the invention: Hair coloring process technical field

[0001] The present invention relates to hair coloring processes. Prior art

[0002] Numerous hair coloring techniques have already been proposed, implementing different types of coloring compositions.

[0003] Furthermore, it is known to use microwave radiation in the field of surface maintenance to enhance the action of detergents. In particular, applications WO 98 / 03621, WO 98 / 03622, WO 98 / 03623, WO 99 / 25802 and WO 99 / 37745 describe treatments for hard surfaces combining exposure to microwave radiation with detergents containing bleaching agents.

[0004] In the field of hair styling, applications DE 3148 538, US 2006 / 0108358, US 2010 / 0006116 or US 2007 / 056860 disclose the direct use of microwave radiation on hair.

[0005] US patents 2006 / 042649 and 6,079,422 describe heatable hair rollers that can be placed in a microwave oven before use for curling hair. These patents describe the process of generating heat using microwaves, but do not involve direct contact between these microwaves and the hair.

[0006] Application WO 2013 / 183021 discloses a process for treating keratin fibers comprising the application of a shaping composition followed by the application of mechanical tension and then exposure to microwave radiation.

[0007] Applications WO 2011 / 141882 and FR 3 062 786 describe hair treatment processes with a mechanical energizing step and a microwave radiation exposure step.

[0008] Application WO 2019 / 122850 discloses a hair coloring process using a coloring composition and simultaneous treatment with radio wave radiation of frequency between 1 MHz and 300 MHz.

[0009] Hair styling and hair coloring usually require two different operations which, on the one hand, lead cumulatively to significant immobilization times and, on the other hand, are not recommended in immediate successive applications due to the risk of denaturing the shades obtained on the hair, with, on the other hand, a significant increase in the risk of damage to the keratin fibers.

[0010] Consequently, in view of these documents, there is still a need to improve hair coloring processes, increasing their effectiveness while preserving the hair fiber as best as possible, and also to propose a process for simultaneous coloring and styling of hair. Description of the invention: Coloring process

[0011] The invention aims to meet this need and relates to a cosmetic hair coloring process comprising at least the steps of:

[0012] a) apply to at least one strand of hair an aqueous coloring composition comprising one or more oxidation dyes and one or more nitrogenous alkali agents,

[0013] b) expose the hair impregnated with the coloring composition to microwave radiation.

[0014] The process according to the invention makes it possible to obtain an improved hair coloring treatment. The use of microwave radiation, while the coloring composition is still present on the hair, provides targeted excitation of the molecules, making it possible to reduce the exposure time for an equivalent result.

[0015] It is also possible to reduce the concentration of oxidation dyes and / or nitrogenous alkali agents used to achieve a given level of colouring.

[0016] The dyeing results are very good, with in particular good coverage of white hair, good tenacity and low selectivity, while limiting damage to the hair.

[0017] The use of microwave radiation makes it possible to accelerate the coloring reaction and therefore to reduce the exposure time required for the composition.

[0018] The durability and homogeneity of the results obtained from the process according to the invention are very good, and the damage to the hair is reduced, the risks of irritation limited.

[0019] Different results are obtained depending on the duration of exposure to microwave radiation, depending in particular on the base color of the hair strand.

[0020] The duration of exposure to microwave radiation can range from 1 second to 30 minutes, better from 1 second to 10 minutes, even better from 1 second to 5 minutes, but preferably from 1 second to 3 minutes.

[0021] The process according to the invention may further comprise a step (d) of shaping the hair, comprising in particular the application of mechanical tension to said strand of hair, via in particular a mechanical tension application device, having a receiving surface intended to receive the strand of hair, including a step of wrapping the strand of hair around a curler.

[0022] The process according to the invention can thus simultaneously contribute to a certain shaping of the hair, and also offers the possibility of carrying out coloring and shaping treatments simultaneously, in a lasting, quick, and satisfactory manner. The curls are well-defined and sufficiently durable, with limited damage.

[0023] In this variant, the shaping step (d) can be carried out before step a) of applying the composition or between step a) and step (b) of exposure to microwave radiation.

[0024] The process according to the invention may further include one or more pre-treatment steps carried out before steps (a) and (b), and / or before or after step (d), as appropriate.

[0025] The process according to the invention may further include one or more post-treatment steps carried out after step (b), and / or after step (c), as appropriate.

[0026] These additional pretreatment or posttreatment steps may include the application of one or more additional compositions other than that present in step (a). The application of these additional compositions may or may not be immediately followed by microwave treatment.

[0027] In the case where a shaping step (d) is performed, the process according to the invention may include a step (e) of applying a hair-shaping composition comprising either one or more film-forming fixing polymers, also called fixing polymers, or one or more agents for breaking the disulfide bonds of keratin, such as thiol reducing agents. Preferably, the process according to the invention does not include such a step (e).

[0028] The process according to the invention may further comprise one or more steps (c) of rinsing the hair, after any one of the steps a), b) and d), preferably a single rinsing step carried out after step (b) of exposure to microwave radiation. Composition

[0029] The colouring composition preferably comprises at least 5% water by weight at room temperature (25°C) and atmospheric pressure (760 mm of mercury).

[0030] The coloring composition may result from a mixture of several compositions, in particular a mixture of a composition comprising one or more oxidizing dyes and one or more nitrogenous alkali agents (al*) and an aqueous composition (al**), comprising in particular at least one oxidizing agent. The aqueous composition (al**) may itself be obtained from a mixture of two or more compositions. The mixing of the compositions is preferably carried out at the time of use of the coloring composition.

[0031] Preferably, the coloring composition (al) comprises at least one agent oxidant.

[0032] Preferably, composition (al) comprises hydrogen peroxide. This hydrogen peroxide may originate from an anhydrous hydrogen peroxide precursor such as urea peroxide, which is present in a composition that hydrolyzes in the presence of composition (al*), or directly from composition (al). More preferably, the hydrogen peroxide may be in the form of an aqueous hydrogen peroxide solution, also called hydrogen peroxide water, present in composition (al**).

[0033] In one embodiment, composition (al) is devoid of oxidizing agents. In this embodiment, the process according to the invention advantageously comprises a step (f) of applying an oxidizing composition after step (b), said oxidizing composition then preferably containing hydrogen peroxide in aqueous medium.

[0034] Preferably, the colouring composition (al) has a pH greater than 7, in particular from 7.1 to 13, better from 7.5 to 12, even better from 8 to 11.

[0035] One or more nitrogenous alkali agents are contained in the composition (al).

[0036] An agent is considered alkaline when introduced into water at temperature At ambient and atmospheric pressure it leads to a weight concentration of 1% at a pH greater than 7.

[0037] The nitrogenous alkali agent(s) contained in the colouring composition (al) are preferably chosen from ammonia and alkanolamines, in particular mono-ethanolamine.

[0038] In the colouring composition (al), the concentration of nitrogenous alkali agents can vary from 0.01% to 20% by weight, better from 0.1% to 15% by weight, even better from 0.5% to 10% by weight relative to the total weight of the composition.

[0039] Preferably, the color composition (al) comprises one or more oxidation bases chosen preferably from among praphenylenediamines, paraaminophenols and heterocyclic bases, such as pyrazoles.

[0040] Even more preferably, the color composition (al) comprises one or more couplers, preferably chosen from among the metadiphenols, the metaaminophenols, the metaphenylenediamines, or the heterocyclic couplers, such as the indoles.

[0041] In the coloring composition (al), the concentration of oxidation dyes can vary from 0.001% to 20% by weight, preferably from 0.01% to 15% by weight, and even better from 0.1% to 10% by weight relative to the total weight of the composition

[0042] The cosmetic compositions used in the process according to the invention may also include at least one compound selected from solvents, siliconed or non-siliconized fats, anionic, cationic, non-ionic or amphoteric surfactants, siliconed or non-siliconized, polymers and in particular anionic, cationic, non-ionic or amphoteric treating or thickening polymers, anti-dandruff agents, or anti-hair loss agents. Microwave radiation

[0043] By "microwaves", one must understand electromagnetic radiation with a frequency ranging from 500 MHz to 300 GHz.

[0044] Preferably, the microwave radiation frequency used in the process of the invention ranges from 500 MHz to 300 GHz, better from 500 MHz to 10 GHz, even better from 900 MHz to 5 GHz, most preferably from 2 GHz to 3 GHz.

[0045] The power of the microwaves used in step b) may be less than or equal to 500 W, preferably from 10 to 300 W, better from 100 to 250 W, even better from 10 to 50 W.

[0046] Preferably, the surface power density on the hair, induced by microwave radiation, can range from 0.1 W / cm2 to 100 W / cm2.

[0047] Exposure to microwave radiation can be achieved using a microwave emitting antenna, said antenna and at least part of the wick to be treated preferably being inserted in a microwave-proof enclosure.

[0048] If necessary, the enclosure, at least during step b), contains the hair to be treated and impregnated with the coloring composition. "Containing the hair" means containing the hair along all or part of its length and over a given width. The enclosure can cover the hair over a length, for example, of 5 cm or more. Thus, a length of at least 5 cm of hair can be treated at one time within the enclosure.

[0049] Said enclosure can be defined at least partially by a housing having a compartment, configured to receive at least part of the hair to be treated and, where appropriate, a hair styling tool, and by a cover pivoting relative to the housing between an open position giving access to the compartment and a closed position, the microwave emitting antenna being disposed inside the compartment.

[0050] In one variant, the enclosure is in the form of a headset.

[0051] The enclosure can be stationary relative to the hair being treated during the emission of microwaves or mobile relative to the hair, allowing a greater length of hair to be treated.

[0052] The enclosure may include at least one seal made of an electrically conductive material, for example, elastically deformable, allowing the microwaves used in step b) to be shielded while allowing the hair to escape from the enclosure. The seal may include a foam charged with electrically conductive particles, a brush made of electrically conductive bristles, or a comb with metal teeth.

[0053] In the case where the speaker is in the form of headphones, the speaker may include a Electromagnetic shielding through which the treated hair can pass. Such shielding allows the user's hair to be treated while protecting their scalp from the emitted microwaves. The electromagnetic shielding is formed, for example, by a grid or a metal mesh. Together

[0054] The invention also relates, according to another aspect, to a hair coloring assembly comprising at least one coloring composition, including one or more oxidation dyes and one or more nitrogenous alkali agents, and a device adapted to expose the hair to microwave radiation as defined above.

[0055] Said device may include a microwave transmitting antenna, said antenna and at least part of the wick to be treated being in particular inserted in a microwave-proof enclosure, as described above.

[0056] Microwaves can be generated inside said device adapted to expose hair to microwave radiation or outside by a microwave generator, for example a solid state generator such as a magnetron.

[0057] In one variant, the generator is located inside the enclosure.

[0058] Microwave emission can be achieved by a non-straight antenna, for example of the helical type.

[0059] The antenna may be made of a sufficiently rigid wire, for example with a diameter of 1 to 3 mm, so as not to require any support or rod for the turns. In one embodiment, the antenna comprises a flexible wire or a conductive track arranged on a support structure, in particular a helical one. This support structure may be made of any dielectric material, preferably PTFE or glass.

[0060] The antenna, when helical, preferably has a fixed helix pitch, for example ranging from 4 to 5 mm. The radius of the helix is ​​preferably constant, for example ranging from 4 to 10 mm. The diameter of the antenna is, for example, 8 to 10 mm.

[0061] The axial extension of the antenna can vary from 50 to 80 mm, preferably from 65 to 75 mm.

[0062] The antenna can be arranged in a tube, in particular closed at one end. This tube can be made of PTFE or another dielectric material.

[0063] The antenna can also be embedded in a dielectric material, preferably flexible, in particular silicone.

[0064] Said device adapted for exposing hair to microwave radiation may include a hair-styling tool, in particular a tool for applying mechanical tension, in particular a curler. The term "curler" refers to a tool for winding hair around the longitudinal axis of the device to a defined diameter, thereby creating mechanical tension that is a function of the diameter. The diameter of said curler may be determined by the desired curling effect.

[0065] The curler may have teeth at the ends of branches which laterally delimit the hair reception surface, said teeth of the curler being advantageously arranged around the antenna.

[0066] The shaping tool can be configured, if necessary, to place the treated hair flat during microwave exposure.

[0067] The removal of mechanical tension on said hair strand is preferably carried out after step b) of exposure to microwave radiation.

[0068] The device may include a housing adapted to receive the shaping tool. This housing may be lined with conductive foam arranged to extend into a hair exit slot. This ensures a good seal, thanks to the deformability of the foam at the slot.

[0069] Where appropriate, the shaping tool and the antenna form a unit assembly which is introduced into the enclosure.

[0070] The shaping tool can be made of PTFE or other dielectric materials, in particular thermoplastics.

[0071] The device used to implement the method according to the invention may include an audible and / or visual warning system, for example to warn the user of a microwave leak outside the enclosure and / or an excessive temperature inside the enclosure.

[0072] The device advantageously includes a safety system preventing the emission of microwaves as long as the enclosure is not closed and / or in the event of abnormal operation, for example microwave leakage and / or excessive temperature.

[0073] The device can be configured to control the duration of microwave emission, so as not to reach a treatment time likely to damage the hair.

[0074] The method according to the invention may include, before step b), a step for detecting the closure of the enclosure. For example, a contactor is activated when the enclosure is closed.

[0075] The emission of microwaves can be conditional upon detection of the enclosure being closed. After emission of microwaves, continued emission of microwaves can be conditional upon the absence of detection of microwave leakage, in particular by means of a microwave-sensitive sensor placed outside the enclosure.

[0076] The process according to the invention may further include a step for detecting the placement of the hair to be processed, before step b). This detection step may be carried out, for example, by an optical sensor and / or a mechanical probe. The detection may also be carried out indirectly, if necessary, by detecting the placement of the shaping tool.

[0077] The process according to the invention may include, for example during step b), a step of measuring the temperature to which the treated hair is subjected. This temperature measurement step may be carried out using a thermometer without contact with the hair.

[0078] The device may include, within the same handpiece, the microwave generator and the shaping tool. The term "handpiece" refers to a part manipulated by the user with one hand during hair treatment.

[0079] The device may include a sensor sensitive to a characteristic of the hair, for example color, mechanical resistance, surface condition, moisture, and the device may control at least one parameter of the treatment according to the characteristic thus detected, for example microwave energy, solvent temperature, treatment time and / or mechanical stress exerted, if applicable.

[0080] The characteristics stated above for the process apply to the assembly, and vice versa. Brief description of the drawings

[0081] The invention will be better understood upon reading the following description and examining the accompanying figures. These are presented only by way of illustration and in no way limit the invention.

[0082] [Fig. 1] [Fig. 1] illustrates different stages of an example of a hair coloring process according to the invention,

[0083] [Fig.2] [Fig.2] schematically and partially represents an example of a device adapted to implement the process according to the invention,

[0084] [Fig.3] [Fig.3] represents the open handpiece of an example of a device adapted to implement the method according to the invention,

[0085] [Fig.4] [Fig.4] represents the handpiece of [Fig.3], closed,

[0086] [Fig. 5] [Fig. 5] represents a shaping tool, once extracted from the part to hand of a variant of a device adapted to implement the method according to the invention, and

[0087] [Fig.6] [Fig.6] is a cross-sectional and side view of a device adapted to implement the process according to the invention and comprising the shaping tool of [Fig.5], when the enclosure is closed. Detailed description

[0088] Various steps of an example of a hair coloring process according to the invention are shown in [Fig.1] and will be described in detail below.

[0089] In this example, during a step 11, an aqueous (al) colouring composition comprising one or more oxidation dyes and one or more nitrogenous alkali agents is applied to at least one strand of hair.

[0090] In step 12, the hair in contact with the coloring composition is exposed to microwave radiation at a frequency greater than or equal to 500 MHz, preferably from 900 MHz to 5 GHz. The duration of exposure to microwave radiation is preferably from 1 second to 3 minutes. The surface power density on the hair, induced by the microwave radiation, can range from 0.1 W / cm² to 100 W / cm².

[0091] The process according to the invention further comprises, in the example described, one or more hair rinsing steps 13, preferably a single hair rinsing step 13 carried out after the microwave radiation exposure step 12.

[0092] The process according to the invention may further comprise a hair styling step 14, including the application of mechanical tension to at least one strand of hair via a mechanical tension application device having a receiving surface for the hair strand, including a step of winding the hair strand onto a curler. This styling step 14 is carried out before step 11, the application of the coloring composition, or between steps 11 and 12.

[0093] The process according to the invention may further comprise one or more pretreatment steps 15 carried out before steps 11 and 12, including for example the application of one or more additional compositions other than that used in step 11.

[0094] One or more post-processing steps 16 may be carried out after step 12 and / or after step 13, including for example the application of one or more additional compositions other than that used in step 11.

[0095] Preferably, and as in the example described, the coloring composition (a1) comprises hydrogen peroxide. The coloring composition may be a mixture of several compositions; in the example considered, it is a mixture of a composition comprising one or more oxidizing dyes and one or more nitrogenous alkali agents (a1*) and an aqueous composition (a1**) comprising said hydrogen peroxide. The mixture of the compositions is prepared at the time of use of the coloring composition. The oxidizing dyes and nitrogenous alkali agents included in the coloring composition (a1) and their concentrations are as described above.

[0096] Figure 2 shows a device 100 adapted for implementing the method according to the invention, comprising a handpiece 3 connected to a base station 1, comprising a microwave generator, by a flexible waveguide 2. The handpiece 3 is intended to be manipulated by the user so as to be placed near the person's head to treat at least one lock of hair H, as illustrated. The handpiece 3 can be made in various ways and defines a microwave-proof processing chamber 4.

[0097] In the example shown in [Fig. 3], the handpiece 3 comprises a housing 10, defining a recess 6, on which a cover 11 is hinged by means of a pin 12. The handpiece is shown closed in [Fig. 4]. The flexible waveguide 2 has only been shown very partially in Figures 3 and following.

[0098] The housing 10 carries an antenna 30 which in the illustrated example is helical in shape, with longitudinal axis 7.

[0099] The antenna 30 is composed in the example considered of a helical metal wire, arranged in a tube 32 of a dielectric material, for example silicone or PTFE.

[0100] The antenna 30 is supported at an axial end of the housing 10 by a flange 14 of the housing 10, with a semi-circular contour.

[0101] The hood 11 has a similar flange 15 on the opposite side, to close the opening 5 of the housing 6, through which a shaping tool can be introduced into the handpiece 3.

[0102] The inner surface of the housing 6 is defined by an electrically conductive coating 7 which reflects microwaves and makes the enclosure 4 microwave-proof. This coating 7 can be made of conductive foam, for example, semi-cylindrical in shape on the cover and housing, disc-shaped for the flange 15 and ring-shaped for the flange 14.

[0103] The housing 10 and the cover 11 define an outlet slot 19 for hair, located at the bottom of a recess 18, on the side opposite the axis 12 of the hinge.

[0104] The coating 7 is preferably projecting into the slot 19, as shown in [Fig. 6], so as to ensure a good seal of the closure despite the passage of hair. The edge of the coating may thus slightly protrude at 17 beyond the edge of the body of the cover and that of the housing to close the slot 19.

[0105] The handpiece 3 includes a hood locking device in the closed position, not shown, as well as an opening detector.

[0106] A temperature detector may be present within the enclosure 4, for example on an internal surface thereof, in order to measure the temperature of the treated hair strand and a control system, for example microprocessor-based, may interrupt or modulate the emission of microwaves in the event of a detected temperature exceeding a predefined threshold.

[0107] In a particular embodiment, the housing 10 defines a recess 6 for receiving a shaping tool, in the example considered being a curler 20, shown in [Fig. 5]. The presence of the tube 32, shown in [Fig. 3], in which the wire of the antenna 30 is arranged, facilitates the insertion of the latter into the curler 20.

[0108] This includes several branches 21 which define a hair receiving surface H, of width L, measured along the longitudinal axis X of the curler 20.

[0109] In this example, the X axis is parallel to the axis of rotation of the hood 11 and coincides with the longitudinal axis 7 of the antenna 30.

[0110] In the example considered, the curler 20 has four arms 21, which are slightly curved towards the X axis and pass through a minimum distance from the X axis at about half its length.

[0111] The branches 21 may have ribs 23 oriented perpendicularly to the X axis to help keep the wick spread over the branches 21, preferably occupying the entire width L in the most uniform way possible.

[0112] The branches 21 connect at their ends to annular parts 25.

[0113] The curler 20 has teeth 26 at the ends of the arms 21, which laterally delimit the hair receiving surface.

[0114] The curler 20 can be made of any dielectric material, preferably PTFE.

[0115] The curler 20 preferably has a symmetrical shape of revolution with respect to to a median plane of symmetry perpendicular to the X axis.

[0116] The curler 20 has pads 27 with enlarged heads, connecting at their base to the corresponding annular parts 25, which bear on the coating 7, as illustrated in [Fig.6], to keep the curler centered in the housing 6.

[0117] The studs 27 are for example located between the teeth 26, as illustrated.

[0118] The width W of the outlet slot 19 for hair can be slightly su greater than L, the length of the housing 6 being substantially equal to the length of the curler 20, so that the latter is immobilized both axially and radially in the housing 6, with a small gap.

[0119] To use the handpiece 3, a strand of hair impregnated with coloring composition is wrapped around the curler 20, then placed inside the housing 10 by moving it laterally relative to it, by introducing it through the opening 5. Then, the cover 11 is closed, and the hair comes out through the slot 19. Once the microwave exposure has been carried out, the strand of hair is extracted by carrying out the operations in reverse order. Examples

[0120] An example of the results obtained by the process according to the invention are summarized in Table 1 below.

[0121] In this example, colour tests were carried out on Caucasian type hair with a tone height of 6 (HT6) and on hair that was 90% naturally white (BN90).

[0122] The compositions used in this example are aqueous coloring compositions (al) according to the invention, resulting from a mixture of a composition comprising one or more oxidizing dyes and one or more nitrogenous alkali agents (al*) and an aqueous composition (al**) comprising at least one oxidizing agent, the mixture of the compositions being prepared at the time of use of the coloring composition (1:1 ratio, preparing 10 g of mixture per gram of hair). More specifically, the compositions used are commercial oxidative coloring products from the Majirel brand, combined with a 20-volume L'Oréal Professionnel brand developer. Shades 6.66, 7.3, and 5 were used, corresponding respectively to an intense red, a golden blonde, and a light brown.

[0123] The colouring composition (al) was applied to both sides of a strand of hair with a brush, the strand thus impregnated then being exposed to microwave radiation of a power of 30 W for 3 minutes.

[0124] The colorimetric parameters observed are Delta E, corresponding to the measurement of the variation in the visual perception of two given colors, before and after treatment by the process of the invention, which can be likened to the rise in color, and the variation in chromaticity, before and after treatment by the process of the invention.

[0125] The results obtained through the implementation of the process according to the invention were compared to results obtained by implementing a prior art coloring process, not using microwave radiation, the hair impregnated with coloring composition being left at room temperature (TA) for 30 minutes.

[0126] [Tab 1] Hair and process used DELTA E CHROMATICITY Prior art: BN90 6.66 TA 30 min 42.98 15.6 Invention: BN90 6.66 p30W 3 min 43.11 14.2 Prior art: HT6 6.66 TA 30 min 17.48 10.4 Invention: HT6 6.66 p30W 3 min 17.19 11.4 Prior art: BN90 5 TA 30 min 43.68 2.4 Invention: BN90 5 p30W 3 min 42.05 4.2 Prior art: HT6 5 TA 21.44 1.6 30 min Invention: HT6 5 p30W 3 min 20.29 2.5 Anterior artery: BN90 7.3 TA 30 min 36.46 10.4 Invention: BN90 7.3 p30W 3 min 34.64 11.25 Anterior artery: HT6 7.3 TA 30 min 12.03 9.9 Invention: HT6 7.3 p30W 3 min 10.13 11.1

[0127]

[0128] Compared to the prior art method, the colorimetric parameters observed remain comparable, the processing time required in the method according to the invention being reduced by a factor of 10.

[0129] Numerous modifications can be made to the processes and devices just described, without departing from the scope of the present invention.

[0130] The invention is not limited to a particular type of shaping tool, or to a particular type of microwave transmitting antenna.

Claims

Demands

1. A cosmetic hair coloring process comprising at least the steps of: a) applying to at least one strand of hair an aqueous coloring composition (al) comprising one or more oxidation dyes and one or more nitrogenous alkali agents, b) exposing the hair impregnated with the coloring composition to microwave radiation.

2. A method according to claim 1, wherein the microwave radiation frequency used in the method of the invention ranges from 500 MHz to 300 GHz, better from 500 MHz to 10 GHz, even better from 900 MHz to 5 GHz, most preferably from 2 GHz to 3 GHz.

3. A method according to any one of the preceding claims, further comprising a step (d) of hair shaping, including in particular the application of mechanical tension to said at least one strand of hair, via in particular a mechanical tension application device, having a receiving surface for receiving the strand of hair, including a step of winding the strand of hair onto a curler, the shaping step (d) preferably being carried out before step (a) of applying the composition or between step (a) and step (b) of exposure to microwave radiation.

4. A method according to any one of the preceding claims, wherein the colouring composition (al) results from a mixture of several compositions, in particular a mixture of a composition comprising one or more oxidation dyes and one or more nitrogenous alkali agents (al*) and an aqueous composition (al**), 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 colouring composition.

5. A method according to any one of the preceding claims, wherein the coloring composition (al) comprises at least one oxidizing agent.

6. A method according to the preceding claim, wherein the colouring composition (al) comprises hydrogen peroxide, in particular in the form of an aqueous solution of hydrogen peroxide present in the composition (al**).

7. A method according to any one of the preceding claims, wherein the colouring composition (al) has a pH greater than 7, in particular from 7.1 to 13, better from 7.5 to 12, even better from 8 to 11.

8. A method according to any one of the preceding claims, wherein the nitrogenous alkali agent(s) contained in the colouring composition (al) are selected from ammonia and alkanolamines, in particular monoethanolamine.

9. A method according to any one of the preceding claims, wherein, in the colouring composition (al), the concentration of nitrogenous alkali agents varies from 0.01% to 20% by weight, better from 0.1% to 15% by weight, still better from 0.5% to 10% by weight relative to the total weight of the composition.

10. A method according to any one of the preceding claims, wherein the coloring composition (al) comprises one or more couplers, preferably selected from metadiphenols, metaaminophenols, metaphenylenediamines, or heterocyclic couplers, such as indoles.

11. A method according to any one of the preceding claims, wherein, in the colouring composition (a1), the concentration of oxidation dyes varies from 0.001% to 20% by weight, better from 0.01% to 15% by weight, still better from 0.1% to 10% by weight relative to the total weight of the composition.

12. A method according to any one of the preceding claims, wherein the exposure to microwave radiation is achieved by means of a microwave emitting antenna, said antenna and at least a part of the wick to be treated being inserted into a microwave-tight enclosure.

13. A method according to any one of the preceding claims, wherein the surface power density on the hair, induced by microwave radiation, ranges from 0.1 W / cm2 to 100 W / cm2.

14. A method according to any one of the preceding claims, wherein the duration of exposure to microwave radiation ranges from 1 second to 30 minutes, better from 1 second to 10 minutes, even better from 1 second to 5 minutes, most preferably from 1 second to 3 minutes.

15. A hair coloring assembly comprising at least one coloring composition, including one or more oxidative colorants and one or more alkali nitrogenous agents, and a device suitable for exposing hair to microwave radiation with frequencies ranging from 500 MHz to 300 GHz, better from 500 MHz to 10 GHz, even better from 900 MHz to 5 GHz, but preferably from 2 GHz to 3 GHz.

16. Assembly according to the preceding claim, wherein the device comprises a microwave emitting antenna (30), said antenna and at least a portion of the wick to be treated being inserted into a microwave-tight enclosure (4).

17. 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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