EP0511892B1 - Method for applying a deformation to hair using a hair curler, and hair curler for working out this method - Google Patents

Abstract

According to the process for applying reshaping to hair by use of a hair-curler, the hair-curler (1) is arranged in such a way that the perimeter along which the lock of hair (M) is rolled increases by approx. 2 to 3% when its temperature rises to pass from a starting temperature to a higher temperature which nevertheless remains lower than a relatively low limit thus avoiding the burning of the hair and/or of the scalp; the longitudinal section of the curler is sufficient to withstand the stresses imposed by elongation of the lock of hair; the lock of hair is rolled around the curler at the starting temperature so that the hair is retained against the hair-curler; the curler is raised to the said higher temperature; the hair is thus subjected to elongation ensuring an increase in the life of the reshaping applied to the hair.

Description

The invention relates to a method for applying a deformation to hair using a curler around which a strand of hair is wound.

Such a process is commonly used to create a waviness on straight hair. To accentuate the wavy effect, wet hair, wound on the curler, can be subjected to heating created either by a dryer hood or equivalent, or by the curler itself, of the heat reserve type.

A process of the same type can be used for straightening strongly wavy hair, for example of the frizzy hair type.

It is known from US Pat. No. 3,623,491 to use a curler for this purpose in which the perimeter along which the wick is wound is capable of being increased by mechanical action.

The object of the invention is, above all, to provide a process of the kind defined above which makes it possible to obtain greater durability of the induced deformation of the hair after it is unwound from the curler

According to the invention, a method for applying a deformation to hair using a curler in which the perimeter around which the strand is wound (M) increases, the hair being thus subjected to an elongation which ensures an increase in the duration in the time of the deformation applied to the hair, characterized in that the curler is arranged so that when its temperature goes from a starting temperature to a higher temperature which however remains below a relatively low limit making it possible to avoid burn them hair and / or scalp, the perimeter of the curler increases by approximately 2 to 3%, the longitudinal section (S) being more than sufficient to withstand the stresses imposed by the stretching of the lock of hair; that the lock of hair is wrapped around the curler at initial temperature so that the hair is held against the curler and that the curler is brought to the above higher temperature, the curler being produced at least in part at using a shape memory material capable of causing said increase in perimeter.

The above temperature limit is not greater than 60 ° C and, preferably, the temperature allowing an increase of approximately 2 to 3% in the perimeter of the curler is of the order of 40 ° C, when the flow temperature is equal to room temperature.

Advantageously, the curler is produced, at least in part, using a shape memory material whose phase transition is located at a temperature below the above limit, the part of the curler is educated in memory material shaped so that the curler turns into a neighboring shaped part, with a perimeter increased by approximately 2 to 3%, when the phase transition temperature is crossed by increasing values.

US-A-4,911,186 has already proposed making a curler out of a shape memory material; however, this prior document only provides for the passage of the curler from a cylindrical shape, for hair winding operations, to a flattened shape facilitating storage.

There is no question of subjecting the hair to a stretch thanks to the curler.

The invention also relates to a curler for implementing the defined method previously, this curler being characterized in that its outer surface has a cross section with a substantially closed outline to allow the winding and tightening of the lock on the curler, this surface comprising a longitudinal slot intended to allow an increase in the perimeter of the cross section, the longitudinal section of the curler being sufficient to absorb the stresses imposed by the stretching of the lock of hair, characterized in that this curler comprises means made of a shape memory material capable of causing an increase in said perimeter about 2 to 3% when the temperature of the curler goes from a starting temperature to a higher temperature with crossing of the phase transition temperature of the shape memory material, this higher temperature remaining below a limit of temperature chosen to avoid burning hair and / or scalp.

Preferably, the shape memory material chosen for the curler has a phase transition temperature of approximately 40 ° C. so that when the curler is brought to this temperature, the above increase in the perimeter of the cross section is obtained. .

According to a first possibility, the curler is formed by a cylindrical piece split longitudinally which is made of a shape memory material and which, when the temperature crosses in increasing direction the phase transition temperature, takes a neighboring cylindrical shape but with a scope increased by approximately 2 to 3%.

According to another possibility, the means made of a shape memory material are constituted by a helical winding of a wire of this material, and the curler comprises several plates made of an inert material, arranged against the helical winding so as to form a sort of prism, these plates remaining free to move relative to one another in being separated by slits along their edges.

Alternatively, the curler includes a hollow cylindrical shell, with a longitudinal slot, in a rigid elastic material while stressing means made of a shape memory material are arranged at least partially inside the envelope to cause an increase in its perimeter when the temperature crosses, by values increasing, that of phase transition of the shape memory material.

The constraint means can be constituted by a plate having a V-shaped cross section, arranged inside the envelope and bearing by its longitudinal edges, against the internal surface of the envelope in substantially diametrically opposite zones. , the plate having been educated to tend to become flat again when the temperature crosses, in the direction of increasing values, the phase transition temperature of the shape memory material constituting this plate, which then causes the opening of the envelope exterior and increasing its diameter.

According to another possibility, the constraint means comprise two parts of conical shape turning their concavity towards the outside and engaged, by their point, in each end of the envelope split longitudinally so as to be in contact with the edge of this end, these parts being mechanically connected to each other by a rigid rod, said conical parts being made of a shape memory material and being educated to tend to open when crossing the phase transition temperature by increasing values, to cause the spacing of the envelope against which they are supported.

As a variant, the conical parts engaged by their point at each end of the envelope and in contact against the edges of these ends are made of an inert material while a bar mechanically connecting the tips of the conical parts is made of a shape memory material and has been educated so as to curve and bring the cones closer together when the phase transition temperature shape memory material is crossed, by increasing values, which causes an increase in the diameter of the envelope.

The shape memory material used can be a metal alloy or a synthetic resin, the phase transition temperature advantageously being around 40 ° C.

Preferably, the shape memory material used supports a mechanical stress of 700 N / mm2; the useful section of the curler is preferably greater than approximately 10 mm 2, which allows the winding of a lock which can include up to approximately 5,000 hairs over a number of turns at most equal to four; for an elongation of the order of 2%, the forces involved can be supported by a curler, the envelope of which is made of such a shape memory material.

The thickness of the envelope is between 0.2 mm and 4 mm approximately.

The invention consists, apart from the arrangements set out above, of a certain number of other arrangements which will be more explicitly discussed below in connection with embodiments described with reference to the attached drawings, but which are in no way limiting.

Figure 1a of the drawing is a cross section of a curler according to the invention, in the shape memory material in the state of rest at room temperature.

Figure 1b is a cross section of the same curler at a temperature higher than that of phase transition.

Figure 1 c is a perspective view of the curler of Figure 1 a , at rest.

Figure 2 is a perspective view of an alternative embodiment of the curler.

Figure 3 is a perspective view of another alternative embodiment of the curler.

Figure 4 is a longitudinal axial section of another alternative embodiment of the curler.

Figure 5, finally, is a longitudinal axial section of another variant.

Referring to FIGS. 1 a and 1 c of the drawings, one can see a winding device 1 for a lock of hair, generally called a curler, constituted by a part 2 of cylindrical, hollow shape, comprising a longitudinal slot 3.

The split cylindrical part 2 is made of a shape memory material, in particular a metal alloy or a synthetic resin having this shape memory effect and whose phase transition temperature is advantageously of the order of 40 ° C. For the envisaged application, this phase transition temperature should be less than a relatively low limit, for example of the order of 60 ° C., to avoid burning the hair or the scalp.

The part 2 is educated to transform, when its temperature is brought to a value exceeding the critical threshold constituted by the phase transition temperature, into a part of neighboring shape whose cross section, represented in FIG. 1 b , has a larger perimeter of around 2 to 3%.

When the phase transition temperature is crossed in the opposite direction, by cooling, the part 2 changes from the shape shown on the 1b to that shown in Figure 1a, that is to say back to its original shape.

Such an increase in the perimeter, from 2 to 3% corresponds to a strong and abrupt variation of dimension for a weak excursion of the temperature. This transformation is reversible so that we find the initial dimensions of the part when it returns to its starting temperature.

Such an increase is much greater than that which could be obtained by the simple thermal expansion of a metallic element, over such a low temperature range.

In practice, if the cylindrical part 2 has an initial diameter of 20 mm, an increase in the width of the slot 3 by 2 mm when the temperature increases from ambient temperature to about 40 ° C, corresponds to a about 3% increase in the perimeter of the cross section.

The hair of the lock M wound and tightened around the part 2 therefore undergoes an elongation of approximately 3% corresponding to the variation in the perimeter of this cylindrical part 2.

The hair of the lock M is clamped against the surface of the part 2 so as to follow the deformations, practically without slipping. Any known fixing means can be provided to hold the curls of hair wound on the curler 2, these means possibly being constituted by an elastic piece P fixed to one end of the curler. The other end of the curler can be secured by clipping or by a hook system with the other free end of the elastic piece P intended to tighten the hair curls on the piece 2.

est suffisante pour supporter les contraintes imposées par l'étirement de la mèche de cheveux M.The useful longitudinal section S of the curler, equal to the product of the length L by the thickness e $\text{(S = Le)}$

is sufficient to withstand the stresses imposed by the stretching of the hair strand M.

The thickness e is advantageously of the order of 0.2 mm, while the length L can be of the order of 50 mm which, when the material constituting the part 2 admits a maximum stress of the order of 700 N / mm2, allows a strand of 1,000 to 5,000 hairs to be wound up to four turns on the device.

A calculation to clarify these explanations is given below.

Consider a part 2 having an initial diameter of 20 mm, at room temperature; the length L is 50 mm and the thickness equal to e .

A strand of n hair ( n being less than 5000) is wound over t turns, t being generally equal to 4.

We can admit that the average diameter of a hair is 0.08 mm which gives an average section of hair of s = 5.10⁻³ mm2. As the average stiffness modulus of a dry hair, the value E s = 4,000 N / mm2 can be adopted and, for a wet hair, the value E h = 1,000 N / mm2, this up to an elongation of approximately 2% of the hair. Beyond this elongation, the rigidity becomes very low.

. Cette force est maximale lorsque les cheveux sont secs ; avec les valeurs données ci-dessus, cette force F atteint 8 000 N pour "epsilon" = 2 %, t = 4 tours et n = 5 000.The resistant force deployed by the lock of hair M when an "epsilon" lengthening is imposed on it is equal to:
$\text{F = [E}\underline{\text{s}}\text{.}\underline{\text{nt}}\text{"epsilon"]}$

. This force is maximum when the hair is dry; with the values given above, this force F reaches 8,000 N for "epsilon" = 2%, t = 4 turns and n = 5,000.

The useful longitudinal section L. e of the winding device 2 must therefore be greater than approximately 11.5 mm2, taking into account a maximum admissible stress of 700 N / mm2.

This results in a length L of 50 mm, a thickness e of about 0.23 mm.

To apply a deformation to hair using the curler 2 of Figures 1a, 1c, we proceed as follows.

A strand M of hair is wound around the curler 2, at the starting temperature, equal to room temperature, for example over four turns, and provision is made either by clamping this strand or using a device clip, holding the wick against the surface of the part 2 to prevent relative sliding of the hair.

The hair curler 2 and the wick M are then subjected to a rise in temperature sufficient to cross the phase transition temperature of the material of the part 2.

The cross section of the part 2 opens as shown in FIG. 1 b by causing a stretching of the hair of the lock M which undergoes, in the example considered, an elongation of approximately 3% corresponding to the variation in the perimeter of the cross section.

Such a deformation is located beyond the flow threshold of the hair, of the order of 2 to 2.5% of elongation, which results in improved performance, in particular with regard to the durability of the deformation. imposed on the hair.

According to the embodiment of Figure 2, the curler 11 comprises a helical winding 12 of a wire made of a shape memory material. This winding is covered by several plates 13 forming a kind of prism, with a hexagonal section in the example considered, separated from each other by longitudinal slots 14 extending along the edges of the prism. The plates 13 are made of an inert material and are free to move around compared to others. The plates 13 are applied against the winding 12 by holding means, not shown, in particular elastic holding means allowing the section to be increased. The plates 13 are strong enough not to deform and impose stretching on the lock of hair wound on these plates. The plates 13 are mounted around the winding 12 so as not to put up any significant resistance to the expansion of this internal winding 12.

The plates 13 are provided to prevent jamming of the hair between the turns of the winding 12.

FIG. 3 shows a curler 21 comprising a cylindrical slotted piece longitudinally made of a rigid, inert elastic material. The slot 23 corresponds to the slot 3 in FIG. 1a . The lock of hair is intended to be wound on this part 22.

Stress means C made of a memory material are placed inside the part 22 to cause an increase in its perimeter when the temperature crosses that of phase transition.

In the example of FIG. 3, the constraint means C is constituted by a plate 24 having a V-shaped cross section, arranged inside the part 22 forming an envelope and bearing by its longitudinal edges 25 against the inner surface of the casing 22 in substantially diametrically opposite zones. The plate 24 has been educated to tend to become flat again when the temperature crosses, by increasing values, the phase transition temperature of the memory material from which this plate 24 is made. Such a deformation causes the opening of the envelope outer 22 and widening of the slot 23 with increase in the perimeter of the cross section. The assembly is arranged so that this increase is of the order of 2 to 3%.

According to the alternative embodiment of FIG. 4, the curler 31 comprises a cylindrical part 32, forming an envelope, made of an inert material, like the part 22 of FIG. 3. This part 32 has a longitudinal slot not visible in FIG. 4. The constraint means C, in the case of FIG. 4, comprises two conical parts 33, 34 provided at each end of the envelope 32, turning their concavity towards the outside and their point inside the envelope. Each piece 33, 34 is in contact with the edge of the end of the envelope. These parts 33, 34 are made of shape memory material and are educated to have a tendency to open when the phase transition temperature is crossed by increasing values. The tips of the parts 33, 34 are mechanically connected to each other by a rigid rod 35 of inert material.

When the temperature of the curler 31 changes from the ambient value to a higher value with crossing of the phase transition temperature, the parts 33, 34 open, as indicated by the arrows in FIG. 4, and, exerting a force on the ends of the part 32, cause the opening of this part and the increase in its diameter and the perimeter of the cross section.

In the embodiment of Figure 5, the curler 41 comprises a cylindrical casing 42, provided with a longitudinal slot not visible in the drawing, made of an inert material. This envelope 42 is similar to the envelopes 22, 32 of FIGS. 3 and 4.

The constraint means C comprises two conical parts 43, 44 made of an inert material, provided at each end of the envelope 42 and turning their concavity towards the outside. The tip of the parts 43, 44 is located inside the envelope 42, the external surface of these parts being in abutment against the edge of the ends of the envelope 42. The points of the parts 43, 44 located at the inside the envelope 42 are mechanically connected to each other by a bar 45 made of shape memory material. The bar 45 has been educated so as to curve and cause the cones 43, 44 to approach, in the axial direction, when the phase transition temperature of the material is crossed, by increasing values. The force exerted by the cones 43, 44 on the ends of the split cylinder 42 causes an increase in the diameter of the envelope 42.

Whatever the embodiment adopted for the hair winding device or curler, the hair is wound on the device at room temperature and then the device is brought to a temperature, preferably of the order of 40 °. C, to obtain an increase of approximately 2 to 3% in the perimeter of the device.

The deformation by stretching communicated to the hair, is located beyond the threshold of flow of the hair (2 to 2.5% of elongation) which improves the durability of the deformation of the hair.

In the case of straight hair subjected to a curling treatment, the curls thus produced last longer.

In the case of a straightening operation for strongly wavy hair (frizzy hair), the durability of the deformation is also improved.

In the description of the exemplary embodiments, a hair curler has essentially been considered designed to work with a flow temperature equal to room temperature.

It is clear that the flow temperature can be lower than the ambient temperature, while the higher temperature can be constituted by the ambient temperature. In such a case, the curler is kept, before use, at the (lower) starting temperature in a refrigerator, for example at a temperature less than or equal to 4 ° C. The rise in temperature then takes place without heating, by change to room temperature.

Claims (16)

1. A method for applying a deformation to hair by using a hair curler, wherein the circumference along which the lock of hair (M) is rolled increases, the hair thus being subjected to an elongation, which ensures an increase in duration of the deformation applied to the hair, characterized in that the hair curler is arranged in such a way that when its temperature passes from an initial temperature to a higher temperature that remains nevertheless below a relatively low limit which makes it possible to avoid burning the hair and/or the scalp, the circumference of the hair curler increases by approximately 2 to 3%, the longitudinal section (S) being, moreover, sufficient to withstand the stresses imposed by the stretching of the lock of hair; that the lock of hair is rolled round the hair curler at the initial temperature so that the hair is kept against the hair curler; and that the hair curler is brought to the above mentioned higher temperature, the hair curler being made at least partly by means of a material with a shape memory that is capable of producing the said increase of the circumference.
2. A method according to claim 1, characterized in that the initial temperature is the ambient temperature.
3. A method according to claim 1, characterized in that the initial temperature is less than the ambient temperature.
4. A method according to claim 2, characterized in that the above mentioned temperature limit does not exceed 60°C; and that the temperature allowing an increase of approximately 2 to 3% of the circumference of the hair curler to be reached is of the order of 40°C.
5. A method according to one of the preceding claims, characterized in that the hair curler (1, 11, 21, 31, 41) is at least partly made by means of a shape memory material whose phase transition is situated at a temperature that is less than the above mentioned limit; and that the part of the hair curler made of a shape memory material is trained for the hair curler to be transformed into a part with a similar shape with its circumference increased by approximately 2-3%, when the phase transition temperature is crossed with increasing values.
6. A hair curler for operating a method according to one of claims 1 to 5, whose outer surface has a cross-section with a substantially closed contour to allow the lock of hair to be rolled and firmly held on the hair curler, this surface including a longitudinal slit (3, 14, 23) intended to allow the circumference of the cross-section to be increased, the longitudinal section (S) of the hair curler being sufficient for absorbing the stresses imposed by the stretching of the lock of hair, characterized in that this hair curler (1, 11, 21, 31, 41) includes means (2; 12; 24; 33, 34; 45) made of a shape memory material capable of producing an increase of the said circumference of approximately 2-3% when the temperature of the hair curler passes from an initial temperature to a higher temperature, when crossing the phase transition temperature of the shape memory material, this higher temperature remaining below a temperature limit chosen to prevent the hair and/or the scalp from being burnt.
7. A hair curler according to claim 6 characterized in that the shape memory material chosen has a phase transition temperature of approximately 40°C.
8. A hair curler according to claim 6 or 7, characterized in that a cylindrical component 2 is formed that is longitudinally slit and made of a shape memory material and which, when the temperature crosses the phase transition temperature in the increasing direction, assumes a similar cylindrical shape but with a circumference increased by approximately 2-3%.
9. A hair curler according to claim 6 or 7, characterized in that the means made of a shape memory material are constituted by a helical winding (12) of a wire made in this material; and that the hair curler has several plates (13) made of an inert material disposed against the helical winding so as to form a kind of prism, these plates remaining free to move relative to each other by being separated from each other by slots (14) along their edges.
10. A hair curler according to claim 6 or 7, characterized in that it comprises a hollow cylindrical shell (22, 32, 42) with a longitudinal slit (23), made of a rigid resilient material, whilst the stressing means (C) made of a shape memory material are disposed at least partly inside the shell (22, 32, 42) so as to produce an increase in its diameter when the temperature crosses that of the phase transition of the shape memory material with increasing values.
11. A hair curler according to claim 10, characterized in that the stressing means (C) is constituted by a plate (24) having a V-shaped cross-section that is disposed inside the shell (22) and bears with its longitudinal edges against the internal surface of the shell in zones that are substantially diametrically opposed, the plate (24) having been trained so as to become flat again when the temperature crosses with increasing values the phase transition temperature of the shape memory material constituting this plate (24), which then produces the opening of the external shell (22) and an increase of its diameter.
12. A hair curler according to claim 10, characterized in that the stressing means (C) include two conical parts turning their concavity towards the outside and being engaged at their tip in each end of the shell (32) that is longitudinally slit, so as to be in contact with the edge of this end, these parts (32, 34) being mechanically connected to each other by a rigid rod (35), the said conical parts (33, 34) being made of a shape memory material and being trained so as to tend to open when the phase transition temperature is crossed with increasing values, so as to cause the shell (32) against which they bear to open out.
13. A hair curler according to claim 10, characterized in that the stressing means (C) include two conical parts (43, 44) made of an inert material, engaged at their tip at each end of the shell (42) and being in contact with the edges of these ends, the tips of these conical parts being mechanically interconnected by a bar (45) made of a shape memory material and trained so as to bend and cause the cones to move towards each other when the phase transition temperature of the shape memory material is crossed with increasing values, which produces an increase in the diameter of the shell.
14. A hair curler according to one of claims 6 to 13, characterized in that the shape memory material used is a metallic alloy or a synthetic resin whose phase transition temperature is situated at approximately 40°C.
15. A hair curler according to one of claims 6 to 14, characterized in that the shape memory material used is intended to withstand a mechanical stress of 700 N/mm² and that the effective longitudinal section of the hair curler is greater than approximately 10 mm².
16. A hair curler according to one of claims 6 to 15, characterized in that the thickness of the shell is comprised between approximately 0.2 mm and 4 mm.

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