Patent Publication Number: US-2022232942-A1

Title: Foil for a strand of keratinic fibers and related kit and illumination process

Description:
The present invention relates to a foil for a strand of keratinic fibers including a first sheet and a second sheet, the first sheet being movable relative to the second sheet between a closed configuration for illumination of the strand and an open configuration. 
     The foil is in particular designed to be used for the treatment of hair. The treatment in particular aims to produce a discoloration of the hair under illumination, or to attach a sheath on the hair that withstands washing in order to give the hair a volume effect. 
     WO 2017/108767, WO 2004/054527 and WO 2007/04872 describe cosmetic sheathing compositions applicable on the hair that include photo-cross-linkable compounds. 
     After application of the sheathing composition on the hair, an illumination device by light-emitting diodes (LED), is passed over the strands of hair to cross-link the polymers and thus to obtain the sheathing. 
     Generally, the emitted light is in the UV-visible domain, at energy doses on the order of the Joule/cm 2 . 
     In other cases, when photo-oxidation must be done to discolor the hair, like in WO 2015/165949, hair treated by a composition comprising a chemical oxidizing agent is subject to the application of light with light-emitting diodes. The illuminating device is generally used at higher powers, for example on the order of around one hundred Joules/cm 2 . 
     Prior to the illumination step, the strands of hair on which the cosmetic composition has been applied are generally isolated from the rest of the hair and contained inside a foil. The foil keeps the sheathing or bleaching composition on the strands of hair and also prevents direct contact between the hair and the illumination device. 
     The aforementioned illumination devices are very effective to offer effective radiation of the strand of hair, while ensuring confinement of the light within the device. 
     However, they are complex to use and generally require the presence of a professional trained to handle such devices. Incorrect handling risks causing a dispersion of light outside the desired treatment zone, which results in deteriorated treatment, and/or an alteration of the hair not treated and a risk for the user. 
     One aim of the invention is therefore to propose a foil for a strand of keratinic fibers that makes it possible to perform treatments requiring an illumination of the strand, while greatly limiting, or even preventing the risks of dispersion of the light. 
     To that end, the invention relates to a foil for a strand of keratinic fibers including a first sheet and a second sheet, the first sheet being connected to the second sheet by an articulation, in particular a hinge, the first sheet being movable relative to the second sheet between a closed configuration for illumination of the strand and an open configuration, characterized in that the first sheet is substantially at least partially transparent to the UV-visible light and in that the second sheet is substantially at least partially opaque to the UV-visible light. 
     According to a variant, the first sheet is substantially transparent to the light, the first sheet preferably having a transmittance greater than 75% in the wavelength region from 350 nm to 500 nm, preferably from 280 nm to 700 nm. According to a variant, the second sheet is substantially opaque to the light, the second sheet preferably having a transmittance of less than 5% in the wavelength range from 350 nm to 500 nm, preferably from 280 nm to 700 nm. 
     The keratinic fibers also receive a maximal illumination, with a reduced loss of light. The bodily surfaces arranged below the foil are further protected. 
     According to a variant, the first sheet and the second sheet each comprise at least a first face and a second face opposite the first face, the first face of the first sheet being at least partially in contact with the first face of the second sheet in the closed configuration. 
     According to a variant, the foil has an optical scale arranged on at least one of the first or the second sheet. 
     The optical scale makes it possible to control the illumination received by the strand of keratinic fibers, and thus to avoid overexposure. 
     According to a variant, the optical scale is arranged on the second face of the second sheet. 
     According to a variant, the optical scale is arranged along the articulation between a first edge and a second edge of the first or the second sheet. 
     The reading of the optical scale by a suitable sensor is made easier. 
     According to a variant, the optical scale comprises a plurality of identical patterns arranged repetitively and separated from one another by a gap that is advantageously constant. 
     The movement of the illumination device along the foil is thus immediately and easily measurable using an optical sensor. 
     According to a variant, the optical scale is obtained by screen printing. 
     The screen printing guarantees an intense color and good opaqueness, facilitating the reading of the optical scale. 
     According to a variant, at least one of the first sheet or the second sheet has a free edge opposite the articulation between the two sheets, the foil further comprising a sealing means arranged along the free edge, the sealing means being able to seal the foil in the closed configuration. The sealing means can for example be made using strips of adhesive or a Velcro system. 
     The strands of keratinic fibers are thus kept between the sheets of the foil during the treatment of the strand by illumination. 
     The articulation between the two sheets can be a gluing or a welding or an adhesive or a stapling or a Velcro device or sewing. It is done along a substantially longitudinal assembly line of the foil. 
     The invention also relates to a kit for a strand of keratinic fibers comprising:
         at least one foil of the aforementioned type, and   a device for illuminating at least one strand of keratinic fibers, the illumination device advantageously comprising a first branch and a second branch defining an illumination cavity, the illumination device comprising an illumination system capable of illuminating the strand.       

     According to one variant, the illumination device comprises an optical system capable of measuring a movement of the illumination device relative to the optical scale if the latter is present. 
     According to one variant, the optical system comprises an optical sensor capable of measuring a movement of the illumination device relative to the optical scale if the latter is present, the optical system being able to control the illumination produced by the illumination system as a function of the movement of the illumination device relative to the optical scale measured by the sensor. 
     According to a variant, the kit further comprises a cosmetic composition for keratinic fibers able to be applied on the strand of keratinic fibers. 
     The invention also relates to a method for treatment of at least one strand of keratinic fibers including the following steps:
         inserting a strand between the first sheet and the second sheet of a foil of the aforementioned type, the foil being in the open configuration;   closing the foil, the strand being between the first sheet and the second sheet;   arranging the foil in the closed configuration such that the first sheet is located opposite an illumination system of an illumination device,   activating the illumination system in order to illuminate the strand; and   performing a relative movement of the illumination device with respect to the foil.       

     According to a variant, the illumination device has an optical sensor arranged so as to measure the movement of the illumination device with respect to an optical scale arranged on at least one of the first sheet or the second sheet of the foil. 
     According to a variant, the optical sensor measures the movement of the illumination device relative to the optical scale, the sensor advantageously controlling the illumination system as a function of said movement. 
     According to a variant, the method comprises, prior to the closing of the foil, or the insertion of the strand into the foil, a step for applying at least one cosmetic composition on the strand. 
     In a variant of this method, the strand is treated beforehand with at least one cosmetic composition. 
     According to a variant, the cosmetic composition comprises at least one chemical oxidizing agent. 
     Preferably, the chemical oxidizing agent is hydrogen peroxide alone or in combination with at least one persalt, and in particular at least one persulfate. 
     Preferably, the composition comprising at least one chemical oxidizing agent comprises at least one alkaline agent. The alkaline agent(s) can be mineral or organic. 
     According to a variant, the cosmetic composition comprises at least one photo-cross-linkable compound, still more preferably a photodimerizable compound. 
     Preferably, the photo-cross-linkable compound is a polymer. Still more preferably, the photo-cross-linkable polymer is a hydrophobized or non-hydrophobized PVA-SBQ. 
     The cosmetic composition comprising the chemical oxidizing agent(s) and/or the photo-cross-linkable compound(s) can also comprise at least one compound chosen from among solvents, fatty bodies that may or may not be siliconized, anionic, cationic, non-ionic or amphoteric surfactants, which may or may not be siliconized, non-photo-cross-linkable polymers, and in particular anionic, cationic, non-ionic or amphoteric treating, fixing or thickening polymers, synthetic or natural soluble coloring agents, pigments, agents breaking disulfide bonds, oxidizing agents, and anti-dandruff agents, loss prevention agents. 
     The composition applied on the hair in the inventive methods can result from mixing during the use of at least two compositions. This is in particular the case for bleaching, where the cosmetic composition applied on the hair preferably results from mixing at the time of the use of two compositions, one of which contains hydrogen peroxide or a hydrogen peroxide precursor, the second composition containing at least one alkaline agent. Still more preferably, the first composition is aqueous and contains hydrogen peroxide, and the second composition is anhydrous. 
     The keratinic fibers are preferably human hair or extensions. 
     According to a variant, the method comprises a step for sealing the foil in the closed configuration prior to the insertion of the foil between the first and second branches of the illumination device. 
     According to a variant, the method comprises a step for sealing the foil in the closed configuration prior to arranging the foil in the closed configuration opposite the illumination system. 
    
    
     
       The invention will be better understood upon reading the following description, provided solely as an example, and in reference to the appended drawings, in which: 
         FIG. 1  is a three-quarters perspective front view of a kit according to the invention during the illumination of the strand of hair, the kit comprising an illumination device and a foil inside which the strand of hair is inserted; 
         FIG. 2  is a schematic perspective view of the foil of  FIG. 1 ; 
         FIG. 3  is a schematic view of a first face of the foil of  FIG. 2 ; and 
         FIG. 4  is a schematic view of a second face of the foil of  FIG. 2 . 
     
    
    
     A kit  10  for a strand of keratinic fibers according to the invention is shown in  FIG. 1 . 
     The kit  10  is designed to illuminate at least one strand  12  of keratinic fibers, for example previously treated by a cosmetic composition. Preferably, the keratinic fibers are hair. 
     In a variant, the cosmetic composition contains at least one photo-cross-linkable polymer that cross-links during the treatment by illumination of the strand  12  by the kit  10 . 
     In a variant, the kit  10  is designed to illuminate the strand  12  of keratinic fibers to bleach the strand  12 , which can be previously treated by a composition containing at least one oxidizing agent. 
     In reference to  FIG. 1 , the kit  10  includes a foil  14  and an illumination device  16  for at least one strand  12  of keratinic fibers. Advantageously, the kit  10  also includes a cosmetic product for keratinic fibers able to be applied on the strand  12  of keratinic fibers. 
     In reference to  FIGS. 2 to 4 , the foil  14  includes a first sheet  20  and a second sheet  22 , the first sheet  20  being connected to the second sheet  22  by means of an articulation  24 , or assembly means  24 , which is for example a gluing or a welding or an adhesive or a stapling or a Velcro device or sewing. The articulation  24  is done along an assembly line. For example, the articulation  24  is a hinge. 
     According to one particular embodiment, the foil  14  further has an optical scale  26  arranged on at least one of the first or the second sheet  20 ,  22 . 
     Advantageously, the foil  14  also comprises a sealing means  28  able to seal the foil  14  in the closed configuration. 
     The first and second sheets  20 ,  22  are able to assume any shape and any dimensions appropriate for the application of a cosmetic product on a strand of hair. In the example illustrated in  FIGS. 1 to 4 , the first and second sheets  20 ,  22  are rectangular. 
     In  FIGS. 2 to 4 , the first sheet and the second sheet  20 ,  22  each have a respective first face  30 ,  31  and second face  32 ,  33 , the second face  32 ,  33  being opposite the corresponding first face  30 ,  31 . In the example illustrated in  FIGS. 2 to 4 , the first faces  30 ,  31  are intended to be in contact with the strand  12  of hair during the illumination of the strand  12  by the illumination device  16 . 
     In a variant, the first sheet  20  extends substantially along a longitudinal axis A-A′, between a first edge  34  and a second edge  36 , and substantially along a first transverse axis normal to the longitudinal axis A-A′, between a free edge  38  and the articulation  24 . 
     The second sheet  22  extends substantially along the longitudinal axis A-A′, between a first edge  35  and a second edge  37 , and substantially along a second transverse axis normal to the longitudinal axis A-A′, between a free edge  39  and the articulation  24 . 
     Preferably, the articulation  24  extends substantially parallel to the longitudinal axis A-A′. 
     In  FIGS. 1 to 4 , the first sheet  20  and the second sheet  22  have the same longitudinal and transverse dimensions. 
     The first sheet  20  and the second sheet  22  each have a length l of between 100 mm and 600 mm, preferably between 120 mm and 450 mm, the length l being measured between the first respective edge  34 ,  35  and the second respective edge  36 ,  37 . 
     The first sheet  20  and the second sheet  22  each have a width L of between 60 mm and 200 mm, preferably between 80 mm and 150 mm, the width L being measured between the respective free edge  38 ,  39  and the articulation  24 . 
     In another variant, the articulation  24  is along the smallest common dimension of the two sheets. 
     In a variant, the first sheet  20  has a length and/or a width different from those of the second sheet  22 . 
     The first sheet  20  has a thickness e of between 10 μm and 100 μm, preferably between 15 μm and 50 μm, the thickness being measured between the first face  30  and the second face  32 . 
     In  FIGS. 2 to 4 , the first sheet  20  is substantially at least partially transparent, preferably completely transparent, to the UV-visible light. “Substantially transparent to the light” means that the first sheet  20  has a transmittance greater than 75% in the wavelength range from 350 nm to 500 nm, preferably from 280 nm to 700 nm, the transmittance being measured via a polychromatic light source and a spectrometer, or via a monochromatic source and a photon counter. This transmittance value is determined at ambient temperature (23° C.+/−5° C.) and at atmospheric pressure (about 1013 hPa). 
     Preferably, the second face  32  of the first sheet  20  is texturized. “Texturized” means that said face  32  has a roughness and is not completely smooth. The roughness allows a multiple reflection of the incident light on the face  32 , leading to a homogeneous diffusion of the light by the first sheet  20 . 
     For example, the second face  32  of the first sheet  20  has a plurality of grooves extending along a main direction, the second face  32  of the first sheet then having a brushed appearance. Said main direction is for example parallel to the first transverse axis. 
     In a variant, the second face  32  of the first sheet  20  has a plurality of grooves extending along at least two directions, the second face  32  then having an abraded appearance. Said roughness promotes the diffusion of the light through the first sheet  20 , while allowing the illumination device  16  to slide over the second face  32  of the first sheet  20 . 
     The first sheet  20  is made from a plastic material. This plastic material is preferably thermoresistive and has a proper resistance up to at least 150° C. This means that the mechanical and optical properties of the material are not damaged at temperatures up to at least 150° C. Still more preferably, this material is a polyethylene terephthalate (designated by the acronym PET). 
     The second sheet  22  has a thickness e′ from 10 μm to 100 μm, preferably from 15 μm to 50 μm, the thickness being measured between the first face  31  and the second face  33 . 
     In a variant, the second face  33  of the second sheet  22  is rough. Said roughness allows the illumination device  16  to slide over the second face  33  of the second sheet  22 . 
     The second sheet  22  is substantially at least partially opaque, preferably completely opaque, to the UV-visible light. The second sheet  22  preferably has a transmittance of less than 5% in the wavelength range from 350 nm to 500 nm, preferably from 280 nm to 700 nm, the transmittance being measured via a polychromatic light source and a spectrometer, or via a monochromatic source and a photon counter. This transmittance value is determined at ambient temperature (23° C.+/−5° C.) and at atmospheric pressure (about 1013 hPa). 
     The second sheet  22  is made from a material chosen from the group made up of opaque plastics (opaque polycarbonates, opaque polyethylenes, opaque polypropylenes, etc.), metals such as aluminums, and paper. 
     The sheets  20 ,  22  can be made up of several layers of different materials as long as the transmittance conditions are respected. 
     Thus, according to one specific embodiment, the second sheet  22  is a sheet of aluminum or paper covered with a plastic coating that ensures better stiffness while maintaining the flexibility. Also preferably, at least one of the first sheet  20  and the second sheet  22  includes at least one liquid-tight layer able to keep a cosmetic product applied on the sheet  20 ,  22  without the product impregnating or passing through the sheet  20 ,  22 . 
     Advantageously, each of the first sheet  20  and the second sheet  22  includes at least one liquid-tight layer arranged and able to keep a cosmetic product applied on the sheet  20 ,  22  without the product impregnating or passing through the sheet  20 ,  22 . 
     It is therefore possible to apply a product on the strand  12  placed on the exposed surface of the sheet  20 ,  22 , in this example the respective first face  30 ,  31  of each sheet  20 ,  22 , without the product passing through the first sheet  20 . 
     Preferably, each of the first sheet  20  and the second sheet  22  is able to withstand high temperatures, typically greater than 150° C. “Able to withstand” means that the mechanical and optical properties of the sheet  20 ,  22  are not damaged. 
     Preferably, when the first  20  and/or the second  22  sheet is made from a plastic material, said first and/or second sheet  20 ,  22  has a glass transition temperature above 80° C. 
     Each of the first sheet  20  and the second sheet  22  is preferably able to withstand the cosmetic products that may be applied on the strand  12 . For example, each of the first sheet  20  and the second sheet  22  is able to withstand products comprising a bleach product, for example an oxidizing product such as hydrogen peroxide. 
     Each of the first sheet  20  and the second sheet  22  preferably has a tearing strength compatible with the passage of the illumination device  16 . 
     The first and the second sheets  20 ,  22  have a good flexibility so as to be able to be folded easily on a strand  12  of hair using the articulation  24 . Preferably, the first sheet  20  has a flexibility substantially identical to the flexibility of the second sheet  22  in order to facilitate the handling of the foil  14 . 
     In  FIGS. 1 to 4 , the articulation  24  is rectilinear and extends along the longitudinal axis A-A′ between the first sheet  20  and the second sheet  22 , preferably over the entire length of the sheets  20 ,  22 . 
     The first sheet  20  is movable relative to the second sheet  22  around the articulation  24  between a closed configuration for illumination of the strand  12  and an open configuration. 
     In the open configuration, the sheets  20 ,  22  are only in contact with one another at the articulation  24 . The first two faces  30 ,  31  are located partially separated from one another and define a receiving area  40  designed to receive at least one strand  12  of keratinic fibers. In the open configuration, the volume of the receiving area  40 , taken between the first two faces  30 ,  31 , is large enough to allow an easy insertion of the strand  12  between the sheets  20 ,  22 . 
     In the closed configuration for illumination of the strand  12 , the sheets  20 ,  22  surrounding the strand  12  are in contact with one another at the articulation  24  and at least part of their respective first face  30 ,  31 . The first faces  30 ,  31  are then located opposite one another and the first transverse axis of the first sheet  20  is substantially parallel to the second transverse axis of the second sheet  22 . The volume of the receiving area  40 , taken between the first two faces  30 ,  31 , is minimal. 
     In  FIGS. 1 to 4 , the optical scale  26  is arranged on the second face  33  of the second sheet  22 . 
     The optical scale  26  extends along the longitudinal axis A-A′, between the first edge  35  and the second edge  37  of the second sheet  22 . 
     In  FIGS. 2 and 4 , the optical scale  26  extends along the articulation  24 . “Along the articulation  24 ” means that the optical scale  26  extends at a distance d from the articulation  24  of less than 10 mm, and preferably 5 mm. 
     Preferably, the position of the optical scale  26  is indicated on the first face  31  of the second sheet  22  using a printed zone  44  across from the optical scale  26 . This indication informs the user of the foil  14  that the hair must not be located at this level, to avoid disrupting the reading by an optical sensor of the illumination device  16 . 
     The optical scale  26  comprises a plurality of patterns  50  arranged repetitively and separated from one another by a gap  52 . 
     The patterns  50  have a different color from that of the second face  33  of the second sheet  22 . 
     In  FIGS. 2 and 4 , the patterns  50  are identical. Each pattern  50  has a rectangular shape. In a variant, the patterns  50  have a circular or elliptical shape. 
     Each pattern  50  has a length l m  of between 3 mm and 40 mm, the length l m  being measured along the second transverse axis. Each pattern  50  has a width L m  of between 0.1 mm and 3 mm, the width L m  being measured along the longitudinal axis A-A′. 
     Preferably, the gap  52  between two adjacent patterns  50  is constant and has a width L i  of between 0.1 mm and 3 mm, the width L i  being measured along the longitudinal axis A-A′. 
     For example, the optical scale  26  is obtained by screen printing. The patterns  50  are made by depositing ink on the second face  33  of the second sheet  22 . 
     The sealing means  28  is arranged along the free edge  38 ,  39  of the first and/or the second sheet  20 ,  22 . For example, the sealing means  28  is an adhesive or a Velcro system arranged along the free edge  38 ,  39 . 
     In  FIG. 3 , each of the first and the second sheet  20 ,  22  has, on its first respective face  30 ,  31 , a glued zone  60  in the form of a strip running along the respective free edge  38 ,  39 . The glued zone  60  extends over the entire length of the free edge  38 ,  39  and has a width L a  of between 1 mm and 10 mm. In a variant, only one of the first and the second sheet  20 ,  22  has, on its first respective face  30 ,  31 , a glued zone  60 . 
     The sealing means  28  prevents keratinic fibers from the strand  12  from leaving the foil  14  laterally when the foil  14  is in the closed illumination configuration. 
     Advantageously, the sealing means  28  is not permanent and the foil  14  is able to go from the closed configuration to the open configuration by ungluing the first sheet  20  and the second sheet  22 . 
     The illumination device  16  for a lock of hair  12  according to the invention is illustrated in  FIG. 1 . The device  16  here is a clamp and is designed to illuminate the strand  12  of hair so as for example to illuminate a strand  12  optionally treated beforehand by a cosmetic composition, for example to bleach it. 
     In reference to  FIG. 1 , the illumination device  16  includes a first branch  100  and a second branch  102 , the branches  100 ,  102  being mounted movably relative to one another, between an open position for introducing the foil  14  into the illumination device  16  and a closed position for confining the foil  14  in an illumination cavity  104  between the first branch  100  and the second branch  102 , visible in  FIG. 1 . 
     The device  16  further includes an assembly  106  for articulating the first branch  100  with the second branch  102  and a system  108  for illuminating the strand  12  in the illumination cavity  104 . 
     According to one specific embodiment, the device  16  further includes an optical system  109  able to measure a movement of the illumination device  16  relative to the optical scale  26 . 
     The first branch  100  extends along a longitudinal axis X-X′ and has a first inner surface delimiting a first side of the illumination cavity  104 . The second branch  102  extends along a longitudinal axis Y-Y′ and has a second inner surface delimiting a second side of the illumination cavity  104 . 
     In this example, the first branch  100  and the second branch  102  are mounted movably relative to one another in rotation, by means of the articulation assembly  106  between the open position and the closed position. The rotation is done about an axis Z-Z′ perpendicular to the longitudinal axis X-X′, Y-Y′ of each branch  100 ,  102 . 
     In the open position of the illumination device  16 , the first branch  100  is partially moved away from the second branch  102 . The volume of the intermediate space between the branches  100 ,  102 , taken between the first inner surface and the second inner surface, is maximal to allow an easy introduction of the foil  14  between the branches  100 ,  102 . 
     In the closed position of the illumination device  16 , visible in  FIG. 1 , the first branch  100  and the second branch  102  are brought closer to one another in order to place their longitudinal axes X-X′ and Y-Y′ substantially parallel to one another. 
     The first inner surface and the second inner surface are then located across from one another. The volume of the intermediate space between the branches  100 ,  102 , taken between the first inner surface and the second inner surface, is then minimal. 
     The illumination system  108  includes at least one light source  110 , and preferably at least one controller  112  of the operation of the or each light source  110 . 
     The light source  110  is mounted on one of the first and the second branch  100 ,  102 , on the inner surface. In  FIG. 1 , the light source  110  is mounted on the first branch  114 . 
     The light source  110  is for example formed by at least one light-emitting diode, preferably by a group of light-emitting diodes. 
     The illumination produced by the light source  110  is preferably produced in the range of wavelengths from 280 nanometers to 700 nanometers, and preferably from 350 to 500 nm. 
     Advantageously, the light source  110  is able to develop a light power from 0.5 Joules/cm 2  to 5000 Joules/cm 2 . 
     To perform these photo-cross-linking and/or treatment operations of a cosmetic composition on the strand  12 , the lighting power will preferably be from 0.5 Joules/cm 2  to 20 Joules/cm 2 . 
     During bleaching operations of the strand  12 , the lighting power will preferably be from 1 Joule/cm 2  to 5000 Joules/cm 2 , preferably from 50 Joules/cm 2  to 2000 Joules/cm 2 , better from 100 Joules/cm 2  to 2000 Joules/cm 2 , still better from 200 Joules/cm 2  to 1000 Joules/cm 2 . 
     The optical system  109  is capable of measuring the movement of the illumination device  16  relative to the optical scale  26  and controlling the illumination produced by the illumination system  108  as a function of the movement of the illumination device  16  relative to the optical scale  26 . 
     According to one embodiment, the optical system  109  includes an optical sensor  120 . 
     The optical sensor  120  is arranged on one of the first and the second branch  100 ,  102 . In  FIG. 1 , the optical sensor  120  is mounted on the second branch  102 . 
     The optical sensor  120  is for example a sensor of the CCD (charge-coupled device) type, or a CMOS (complementary metal-oxide semiconductor) sensor. Advantageously, the optical sensor  120  is associated with a timing system able to measure the time. 
     A control module  122  can be configured to control the level of illumination produced by the illumination system  108 . 
     For example, as a function of the data measured by the optical sensor  120 , the control module  122  is configured to transmit an illumination instruction to the illumination system  108 , in particular to the controller  112 , the instruction being the maintenance, increase or decrease of the level of illumination, or even the elimination of the illumination. 
     For example, when a movement measured by the optical sensor  120  is below a minimum authorized value for a defined time, the control module  122  transmits a instruction to the illumination system  108 , such that the level of illumination of the strand  12  is decreased or eliminated, in order to prevent the strand  12  from being overexposed. 
     Conversely, when a movement measured by the optical sensor  120  is above a maximum authorized value for a defined time, the control module  122  transmits a instruction to the illumination system  108 , such that the level of illumination of the strand  12  is increased, in order to prevent the strand  12  from being underexposed. 
     The minimum authorized value and the maximum authorized value are potentially adjustable by the user, for example from an adjusting device arranged on one of the branches  100 ,  102  of the illumination device  16 . These values are for example adjustable as a function of the type of hair or the selected treatment (sheathing or bleaching). 
     In the example of  FIG. 1 , the optical system  109  includes a memory  124  and a processor  126  associated with said memory  124 . 
     The control module  122  can implement software, or a software component, executable by the processor  126 . The memory  124  of the optical system  109  is then able to store software for establishing an illumination instruction and software for transmitting at least one illumination instruction to the illumination system  108 , in particular to the controller  112 . The processor  126  is then able to execute each of the establishing software and the transmission software. 
     The operation of the kit  10  for a strand  12  of keratinic fibers will now be described. 
     Initially, the user places the foil  14  in the open position and grasps a strand  12  of hair intended to undergo an illumination. 
     In the case of a photo-cross-linking treatment, the strand  12  has, prior to illumination, been coated with a cosmetic composition containing at least one photo-cross-linkable compound. 
     In the case of a bleaching treatment, the strand  12  has, prior to illumination, for example been coated with a cosmetic composition containing at least one oxidizing compound. 
     The user then inserts the strand  12  between the first sheet  20  and the second sheet  22  of the foil  14  across from the first faces  30 ,  31 . 
     Then, the user transitions the foil  14  to its closed illumination position by bringing the first sheet  20  and the second sheet  22  closer to one another. 
     When the foil  14  includes a sealing means  28 , the latter is implemented in order to prevent the keratinic fibers of the strand  12  from leaving the receiving area  40  during the passage of the illumination device  16 . 
     Then, the user places the illumination device  16  in the open position and inserts the foil  14  between the first branch  100  and the second branch  102  in the illumination cavity  104 , such that the first sheet  20  is located opposite the light source(s). 
     The optical scale  26 , if it is present, is placed opposite the optical system  109 , such that the optical system  109  is able to measure the movement of the illumination device  16  relative to the optical scale  26 . 
     Then, the user transitions the illumination device  16  to its closed position by bringing the first branch  100  and the second branch  102  closer to one another. During this approach, the inner surface of the first branch  100  is placed across from the inner surface of the second branch  102  to close the illumination cavity  104 . 
     The user then activates the light source  110 . The controller  112  controls the light source  110  to apply the desired illumination on the strand  12 . 
     Then, the user moves the illumination device  16  along the foil  14  in order to treat the strand  12  over a chosen length. 
     The optical system  109 , when it is present, uses the optical sensor  120  to measure the movement of the illumination device  16  relative to the optical scale  26 . 
     The control module  122  then controls the level of illumination produced by the illumination system  108 . 
     When the movement measured by the optical sensor  120  is between the maximum authorized value and the minimum authorized value for a defined time, the control module  122 , in particular the processor  126 , sends a maintenance instruction of the level of illumination to the controller  112 . 
     When the movement measured by the optical sensor  120  is above the maximum authorized value, that is to say, when the user passes the illumination device  16  over the foil  14  too quickly, the control module  122 , in particular the processor  126 , transmits an instruction to increase the level of illumination to the controller  112 . Said controller  112  then increases the illumination power of the light source  110 . It is therefore not necessary to perform several passes of the illumination device  16  along the foil  14  in order to obtain the desired illumination. 
     When the movement measured by the optical sensor  120  is below the minimum authorized value, that is to say, when the user passes the illumination device  16  over the foil  14  too slowly, the control module  122 , in particular the processor  126 , transmits an instruction to decrease the level of illumination to the controller  112 . Said controller  112  then decreases the illumination power of the light source  110  in order to avoid overexposing the strand  12 . 
     A regular illumination level of the strand  12  is thus maintained during the passage of the illumination device  16  over the foil  14 , independently of the passage speed of the illumination device  16  relative to the strand  14 . 
     Then, the user opens the illumination device  16  again in order to remove the strand  14 . 
     Optionally, the user places another foil  14  between the branches  100 ,  102  or uses the same foil  14  with a different strand  12 . 
     The kit  10  according to the invention is thus easy to use. 
     Even in the case of incorrect use, for example by a passage of the illumination device  16  too fast or too slow, the level of illumination experienced by the strand  12  is constant along the strand  12 , ensuring an optimal treatment of the keratinic fibers. 
     The foil  14  according to the invention limits the risk of light leaking outside the desired treatment zone, which can result in deteriorated treatment, and/or an alteration of the hair not treated and/or a risk for the user. 
     When the foil  14  has an optical scale  26 , the foil  14  according to the invention limits, when it is used with the illumination device  16 , the risk of the keratinic fibers of the strand  12  being overexposed during the illumination, which would cause them to be altered, or conversely the risk of them being underexposed with an insufficient technical result, which would then potentially require several passes of the illumination device  16 , with a risk of not controlling the total illumination received by the strand  12 . 
     In a variant, the sheets  20 ,  22  each have a non-rectangular shape, for example with a circular, oval or elliptical contour, as long as they have dimensions making it possible to apply a product on a strand of hair ergonomically. 
     In a variant, the patterns of the optical scale are not all identical. For example, the patterns have a length increasing between the first edge  35  and the second edge  37 . This allows the illumination device  16  to know its location relative to the foil  14  along the longitudinal axis A-A′, and optionally to adapt the level of illumination of the strand as a function of this location, for example to produce shading effects along the strand  12 . 
     In a variant, not shown, the foil  14  has no articulation between the first sheet  20  and the second sheet  22 . Only the differences with respect to the foil  14  comprising an articulation as described above will be described in detail below. 
     In this variant, the first sheet  20  extends substantially along a first longitudinal axis, between a first edge and a second edge, and substantially along a first transverse axis normal to the first longitudinal axis, between a first free edge and a second free edge. The second sheet  22  extends substantially along a second longitudinal axis, between a first edge and a second edge, and substantially along a second transverse axis normal to the second longitudinal axis, between a first free edge and a second free edge. 
     The widths of the first sheet  20  and the second sheet  22  are then measured between the first respective free edge and the second respective free edge. 
     The first sheet  20  is movable relative to the second sheet  22  between a closed configuration for illumination of the strand  12  and an open configuration. 
     In the open configuration, the first two faces  30 ,  31  are located separated from one another and define a receiving area  40  designed to receive at least one strand  12  of keratinic fibers. In the open configuration, the volume of the receiving area  40 , taken between the first two faces  30 ,  31 , is large enough to allow an easy insertion of the strand  12  between the sheets  20 ,  22 . 
     In the closed configuration for illumination of the strand  12 , the sheets  20 ,  22  surrounding the strand  12  are in contact with one another on at least part of their respective first face  30 ,  31 . The first faces  30 ,  31  are then located across from one another. The first longitudinal axis of the first sheet  20  is then substantially parallel to the second longitudinal axis of the second sheet  22  and the first transverse axis of the first sheet  20  is substantially parallel to the second transverse axis of the second sheet  22 . The volume of the receiving area  40 , taken between the first two faces  30 ,  31 , is minimal. 
     In this embodiment, the optical scale  26  extends along a free edge. “Along the free edge” means that the optical scale  26  extends at a distance d from said free edge of less than 10 mm, and preferable 5 mm.