Patent Application
20210204667
The invention relates to an ultrasound hair care device and method for drying and styling hair.
Many women are concerned about hair damage resulting from styling and are sometimes dissatisfied with the results obtained from present styling devices. In general, there is awareness that applying heat to the hair will cause damage. The term hair styling as used herein is intended to encompass all actions such as hair crimping, curling, perming and straightening.
Traditional electrical hair styling devices use hot irons designed to give a thermal treatment to the hair fibers or lock of fibers while pressing them into a desired shape. The combination of excessive heating and/or weathering with mechanical (shear) forces during styling and combing leads to moisture loss and potential hair damage. Another problem is styling when hair is still damp or wet. This can create additional damage to the hair structure or might decrease the efficacy of the treatment.
US 2012/0291797 discloses a hair styling apparatus that includes a hair-heating device for applying heat to hair. The hair-heating device has a moisture-temperature setting and a dry-temperature setting less than moisture-temperature setting. A moisture sensor detects a moisture-indicating parameter of the hair, and generates a moisture-indicating signal indicative of whether the hair is at or below a predetem 1 ined moisture threshold level. A control circuit adjusts the temperature of the hair-heating device from the moisture-temperature setting to the dry-temperature setting in response to the moisture sensor generating a moisture indicating signal indicative of the hair being at or below the predetermined moisture threshold level. The hair-heating device is active in the dry-temperature setting.
US 2012/0312320 mentions that some hair styling tools incorporate the distribution of steam, ultrasonic waves, or active hair treatment compositions in addition to the application of heat, and that there are various methods for measuring moisture content in hair via observing electrical conductance, impedance, resistance, ultrasound, etc. No details are mentioned.
US 2006/0272669 discloses hair styling appliances that utilize ultrasonic vibration for hair styling, and mentions that it is possible to atomize moisture inside hair to evaporate the moisture by ultrasonic vibration, even under room temperature. It is thus not necessary to use an extremely high temperature (e.g., 130° C.) in order to evaporate moisture inside hair, which high temperature causes denaturation of protein and scald.
It is, inter alia, an object of the invention to provide a practical ultrasound hair care device and method for drying and styling hair. The invention is defined by the independent claims. Advantageous embodiments are defined in the dependent claims.
The present invention is based on the new insight that nebulizing (the water for drying the hair) and styling with optimized but distinctively different ultrasound frequencies have significant benefits over using a single frequency range for both styling and drying with ultrasound. Moreover, styling can only be done in an optimal way when the hairs are dry. Drying the hairs before styling makes the styling to be performed at higher temperature which results in better retention of style and quicker styling so hairs will be exposed to high temperature for shorter periods of time. Both conventional and surface acoustic wave based ultrasound nebulization elements can be implemented in the haircare device.
A first aspect of the invention provides an ultrasound hair care device for drying and styling hair. An ultrasound unit applies ultrasound to the hair. A hair moisture measurement unit measures a moisture level of the hair. A control unit controls the ultrasound unit based on the moisture level. In accordance with the present invention, ultrasound is applied to the hair at a first frequency not exceeding 1 MHz for drying the hair, and/or at a second frequency of at least 1 MHz for styling the hair in dependence on the moisture level.
Advantageously, the first frequency does not exceed 0.5 MHz, and preferably does not exceed 0.4 MHz. The second frequency is advantageously at least 5 MHz, and preferably between 6.4 MHz and 500 MHz.
An ultrasound intensity is advantageously at least 1 W/cm2, and preferably does not exceed 10 W/cm2.
The control unit may comprise a look-up-table for switching the ultrasound unit to operate at the first frequency and/or at the second frequency in dependence on the moisture level.
A second aspect of the invention provides a hair care method of drying and styling hair, the hair care method comprising measuring a hair moisture level; and applying ultrasound to the hair at a first frequency not exceeding 1 MHz for drying the hair and/or at a second frequency of at least 1 MHz for styling the hair in dependence of the hair moisture level.
Advantageously, ultrasound is applied during a period not exceeding 2 minutes, and preferably not exceeding 1 minute.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
Nebulization by means of ultrasound can be achieved within a frequency range of 20 kHz-1 MHz. To prevent cavitation, a frequency range of 20 kHz-0.4 MHz is preferably selected. Styling by means of ultrasound can be achieved within a frequency range of 1 MHz-500 MHz. To prevent cavitation, a frequency range of 6.4 MHz-500 MHz could be selected. Finally, moisture sensing by means of ultrasound can be achieved within a frequency range of 100 kHz to 1 MHz. The preferred range of intensity of an effective ultrasound-based hair styling device is between 1 W/cm2 and 10 W/cm2 measured at the transducer-hair interface.
Three mechanisms of ultrasound styling have been proposed:
Heating; the hydrogen bonds are broken by increasing the temperature of the hairs above the glass transition temperature of hair.
Cavitation+heat; cavitation can decrease the power needed for styling with heat only
Non-thermal (i.e. mechanical vibrations); experiments have shown ultrasound as a means to break hydrogen bonds without using heat. Not using heat is a big advantage in order to avoid overheating during styling.
As shown in
Curve A shows the threshold for styling through ultrasound heating (assuming all power is absorbed by hairs, 60 s).
Curve B shows the threshold for styling through ultrasound heating (60% relative humidity, matched to experiments, 60 s).
Curve C shows the threshold for nebulization (typical water film thickness), and curves C1-C2 show thresholds for nebulization (limits for 2-10 μm water film thickness).
Curve D shows the threshold for cavitation.
Region 1 is a preferred region for ultrasound based styling (heating+cavitation).
Region 2 is a preferred region for ultrasound based drying (nebulization).
Region 3 is a preferred region for ultrasound based styling & drying.
Region 4 is a preferred region for ultrasound based styling (heating).
For cavitation to take place at least a thin film of liquid has to be present on the hairs. During the drying phase cavitation can play a role to enhance the drying process. Styling should preferably only take place once the hair has fully dried to prevent cavitation from happening. Especially at higher power cavitation can damage the hair structure. In this case two non-overlapping frequencies are preferred for several reasons:
We favor styling through ultrasound heating and/or non-thermal without cavitation. (Region 4). Cavitation may decrease the power needed, but it also brings increased risk of damaging the hairs (Region 1). We do not exclude to use cavitation for styling, but preferably it is not used.
Drying through nebulization with high power using cavitation can be damaging to the hairs and therefore a more gentle form of nebulization is preferred (Region 2). We do not exclude to use cavitation to increase nebulization speed, but preferably it is not used.
A combined ultrasound styling & drying effect requires a very narrow frequency range and a setup with little losses (Region 3). The threshold for styling through ultrasound heating will lie somewhere between the threshold as predicted by 100% absorption of ultrasound power in hairs (Curve A) and less efficient absorption of ultrasound power in hairs as found in experiments (Curve B), thus significantly shrinking the preferred region for ultrasound based styling & drying (Region 3). Variation in moisture content, relative humidity, hair density, hair diameter, volume etc. will all influence the preferred region for ultrasound based styling and drying, making it very hard to predict the right settings let alone to predetermine said parameters to fall in a viable frequency range for styling and drying. Therefore, in practice the preferred regions for styling (Region 2) or drying (Region 4) are better defined and more robust than the preferred region for styling and drying (Region 3).
The hair care device can then be made to be safe for use if it is carefully designed such that:
During operation, the transducer does not touch the skin/scalp;
During operation, there is a substantial distance between the transducer and skin/scalp, wherein within the distance a material with low acoustic impedance e.g. air, is present to allow reflection of any leaking ultrasound wave in the interface to the skin due to acoustic impedance mismatch, limiting the ultrasound intensity of more than 3 W/cm2 to reach the skin, and;
During non-operation, the transducer does not emit ultrasound.
Piezoelectric crystals (PMUT or standard) are used to produce ultrasound (>20 kHz). Non-piezoelectric techniques like Capacitance Micro-machined Ultrasonic Transducers (CMUT) can be used for higher frequencies (typically up to ˜100 MHz) and can be used with this invention. These techniques use relatively small transducers and are cheaper, thereby making it attractive for both home use and semi-professional hair care applications.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. If CMUT transducers are used, a single ultrasound transducer may be used for both ultrasound frequencies. It is possible to have a hard switch between the different ultrasound frequencies in that below a certain moisture level the first frequency is produced while above that moisture level the second frequency is produced. It is alternatively possible to have a soft switch allowing for a gradual reduction of the intensity of the ultrasound produced at the first frequency, and a gradual increase of the intensity of the ultrasound produced at the second frequency, as a result of a decreasing moisture level of the hair. In such a soft switching embodiment, a look-up table is preferably used in the control unit for determining the intensities of the ultrasound produced at the first and second frequencies in dependence of the moisture level.
In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and/or by means of a suitably programmed processor. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16156168.3 | Feb 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/053461 | 2/16/2017 | WO | 00 |
